There is test host with two test items with simple trigger on each and connected to Inventory. 

Host – TestHost.
Zabbix trapper items: 
TestInt as int, connected to “Tag” inventory field 
TestStr as string connected to “serialno_a”.
History was set first time for a 90 days. 

Triggers are very easy: 
TestIntT {TestHost:TestInt.last()}<10 
TestStrT {TestHost:TestStr.diff(0)}=1.

Data was sent via zabbix_sender. 

I got data via API to keep space from screenshots.
Script “test.sh” is bellow data logs. 

1. Sending initial data. 

[skuksa@opmon01 zabbix]$ zabbix_sender -z 127.0.0.1 -s TestHost -k TestInt -o 100
info from server: "processed: 1; failed: 0; total: 1; seconds spent: 0.000085"
sent: 1; skipped: 0; total: 1
[skuksa@opmon01 zabbix]$ zabbix_sender -z 127.0.0.1 -s TestHost -k TestStr -o "TestValue"
info from server: "processed: 1; failed: 0; total: 1; seconds spent: 0.000144"
sent: 1; skipped: 0; total: 1
[skuksa@opmon01 zabbix]$ zabbix_sender -z 127.0.0.1 -s TestHost -k TestInt -o 100
info from server: "processed: 1; failed: 0; total: 1; seconds spent: 0.000085"
sent: 1; skipped: 0; total: 1
 [skuksa@opmon01 zabbix]$ zabbix_sender -z 127.0.0.1 -s TestHost -k TestStr -o "TestValue"
info from server: "processed: 1; failed: 0; total: 1; seconds spent: 0.000113"
sent: 1; skipped: 0; total: 1

2. Check host params.

[skuksa@opmon01 zabbix]$ ./test.sh
      ["name"]=>
      string(8) "TestHost"
          ["itemid"]=>
          string(15) "100100000023884"
          ["name"]=>
          string(7) "TestInt"
          ["key_"]=>
          string(7) "TestInt"
          ["history"]=>
          string(2) "90"
          ["description"]=>
          string(0) ""
          ["lastvalue"]=>
          string(3) "100"
          ["prevvalue"]=>
          string(3) "100"
          ["itemid"]=>
          string(15) "100100000023883"
          ["name"]=>
          string(7) "TestStr"
          ["key_"]=>
          string(7) "TestStr"
          ["history"]=>
          string(2) "90"
          ["description"]=>
          string(0) ""
          ["lastvalue"]=>
          string(9) "TestValue"
          ["prevvalue"]=>
          string(9) "TestValue"
        }
        ["serialno_a"]=>
        string(9) "TestValue"
        ["tag"]=>
        string(3) "100"

      ["triggerid"]=>
      string(15) "100100000013631"
      ["expression"]=>
      string(20) "{100100000013098}<10"
      ["description"]=>
      string(8) "TestIntT"
      ["value"]=>
      string(1) "0"
      ["priority"]=>
      string(1) "2"
      ["functions"]=>
      array(1) {
          ["functionid"]=>
          string(15) "100100000013098"
          ["itemid"]=>
          string(15) "100100000023884"
          ["triggerid"]=>
          string(15) "100100000013631"
          ["function"]=>
          string(4) "last"
      ["triggerid"]=>
      string(15) "100100000013630"
      ["expression"]=>
      string(19) "{100100000013097}=1"
      ["description"]=>
      string(8) "TestStrT"
      ["value"]=>
      string(1) "0"
      ["priority"]=>
      string(1) "1"
      ["functions"]=>
      array(1) {
          ["functionid"]=>
          string(15) "100100000013097"
          ["itemid"]=>
          string(15) "100100000023883"
          ["triggerid"]=>
          string(15) "100100000013630"
          ["function"]=>
          string(4) "diff"

3. Îę, values correct, Inventory data is correct, triggers state is correct.
4. Sending data to activate triggers. 

[skuksa@opmon01 zabbix]$ zabbix_sender -z 127.0.0.1 -s TestHost -k TestStr -o "TestValue1"
info from server: "processed: 1; failed: 0; total: 1; seconds spent: 0.000054"
sent: 1; skipped: 0; total: 1
[skuksa@opmon01 zabbix]$ zabbix_sender -z 127.0.0.1 -s TestHost -k TestInt -o 1
info from server: "processed: 1; failed: 0; total: 1; seconds spent: 0.000059"
sent: 1; skipped: 0; total: 1

5. Check result

[skuksa@opmon01 zabbix]$ ./test.sh
      ["name"]=>
      string(8) "TestHost"
          ["itemid"]=>
          string(15) "100100000023884"
          ["name"]=>
          string(7) "TestInt"
          ["key_"]=>
          string(7) "TestInt"
          ["history"]=>
          string(2) "90"
          ["description"]=>
          string(0) ""
          ["lastvalue"]=>
          string(1) "1"
          ["prevvalue"]=>
          string(3) "100"
          ["itemid"]=>
          string(15) "100100000023883"
          ["name"]=>
          string(7) "TestStr"
          ["key_"]=>
          string(7) "TestStr"
          ["history"]=>
          string(2) "90"
          ["description"]=>
          string(0) ""
          ["lastvalue"]=>
          string(10) "TestValue1"
          ["prevvalue"]=>
          string(9) "TestValue"
        }
        ["serialno_a"]=>
        string(10) "TestValue1"
        ["tag"]=>
        string(1) "1"

      ["triggerid"]=>
      string(15) "100100000013631"
      ["expression"]=>
      string(20) "{100100000013098}<10"
      ["description"]=>
      string(8) "TestIntT"
      ["value"]=>
      string(1) "1"
      ["priority"]=>
      string(1) "2"
      ["functions"]=>
      array(1) {
          ["functionid"]=>
          string(15) "100100000013098"
          ["itemid"]=>
          string(15) "100100000023884"
          ["triggerid"]=>
          string(15) "100100000013631"
          ["function"]=>
          string(4) "last"
      ["triggerid"]=>
      string(15) "100100000013630"
      ["expression"]=>
      string(19) "{100100000013097}=1"
      ["description"]=>
      string(8) "TestStrT"
      ["value"]=>
      string(1) "1"
      ["priority"]=>
      string(1) "1"
      ["functions"]=>
      array(1) {
          ["functionid"]=>
          string(15) "100100000013097"
          ["itemid"]=>
          string(15) "100100000023883"
          ["triggerid"]=>
          string(15) "100100000013630"
          ["function"]=>
          string(4) "diff"

6. Ok, it works good, all correct. Sending data to clear triggers. 

[skuksa@opmon01 zabbix]$ zabbix_sender -z 127.0.0.1 -s TestHost -k TestInt -o 1000
info from server: "processed: 1; failed: 0; total: 1; seconds spent: 0.000051"
sent: 1; skipped: 0; total: 1
[skuksa@opmon01 zabbix]$ zabbix_sender -z 127.0.0.1 -s TestHost -k TestStr -o "TestValue1"
info from server: "processed: 1; failed: 0; total: 1; seconds spent: 0.000051"
sent: 1; skipped: 0; total: 1
[skuksa@opmon01 zabbix]$ ./test.sh
      ["name"]=>
      string(8) "TestHost"
          ["itemid"]=>
          string(15) "100100000023884"
          ["name"]=>
          string(7) "TestInt"
          ["key_"]=>
          string(7) "TestInt"
          ["history"]=>
          string(2) "90"
          ["description"]=>
          string(0) ""
          ["lastvalue"]=>
          string(4) "1000"
          ["prevvalue"]=>
          string(1) "1"
          ["itemid"]=>
          string(15) "100100000023883"
          ["name"]=>
          string(7) "TestStr"
          ["key_"]=>
          string(7) "TestStr"
          ["history"]=>
          string(2) "90"
          ["description"]=>
          string(0) ""
          ["lastvalue"]=>
          string(10) "TestValue1"
          ["prevvalue"]=>
          string(10) "TestValue1"
        ["serialno_a"]=>
        string(10) "TestValue1"
        ["tag"]=>
        string(4) "1000"

      ["triggerid"]=>
      string(15) "100100000013631"
      ["expression"]=>
      string(20) "{100100000013098}<10"
      ["description"]=>
      string(8) "TestIntT"
      ["value"]=>
      string(1) "0"
      ["priority"]=>
      string(1) "2"
      ["functions"]=>
      array(1) {
          ["functionid"]=>
          string(15) "100100000013098"
          ["itemid"]=>
          string(15) "100100000023884"
          ["triggerid"]=>
          string(15) "100100000013631"
          ["function"]=>
          string(4) "last"
      ["triggerid"]=>
      string(15) "100100000013630"
      ["expression"]=>
      string(19) "{100100000013097}=1"
      ["description"]=>
      string(8) "TestStrT"
      ["value"]=>
      string(1) "0"
      ["priority"]=>
      string(1) "1"
      ["functions"]=>
      array(1) {
          ["functionid"]=>
          string(15) "100100000013097"
          ["itemid"]=>
          string(15) "100100000023883"
          ["triggerid"]=>
          string(15) "100100000013630"
          ["function"]=>
          string(4) "diff"

7. Ok, it works good, all correct. 
8. Now change configuration and set history to 0 and wait configuration sync. 
9. Check new config. 

[skuksa@opmon01 zabbix]$ ./test.sh
      ["name"]=>
      string(8) "TestHost"
          ["itemid"]=>
          string(15) "100100000023884"
          ["name"]=>
          string(7) "TestInt"
          ["key_"]=>
          string(7) "TestInt"
          ["history"]=>
          string(1) "0"
          ["description"]=>
          string(0) ""
          ["lastvalue"]=>
          string(4) "1000"
          ["prevvalue"]=>
          string(1) "1"
          ["itemid"]=>
          string(15) "100100000023883"
          ["name"]=>
          string(7) "TestStr"
          ["key_"]=>
          string(7) "TestStr"
          ["history"]=>
          string(1) "0"
          ["description"]=>
          string(0) ""
          ["lastvalue"]=>
          string(10) "TestValue1"
          ["prevvalue"]=>
          string(10) "TestValue1"
        ["serialno_a"]=>
        string(10) "TestValue1"
        ["tag"]=>
        string(4) "1000"

      ["triggerid"]=>
      string(15) "100100000013631"
      ["expression"]=>
      string(20) "{100100000013098}<10"
      ["description"]=>
      string(8) "TestIntT"
      ["value"]=>
      string(1) "0"
      ["priority"]=>
      string(1) "2"
      ["functions"]=>
      array(1) {
          ["functionid"]=>
          string(15) "100100000013098"
          ["itemid"]=>
          string(15) "100100000023884"
          ["triggerid"]=>
          string(15) "100100000013631"
          ["function"]=>
          string(4) "last"
      ["triggerid"]=>
      string(15) "100100000013630"
      ["expression"]=>
      string(19) "{100100000013097}=1"
      ["description"]=>
      string(8) "TestStrT"
      ["value"]=>
      string(1) "0"
      ["priority"]=>
      string(1) "1"
      ["functions"]=>
      array(1) {
          ["functionid"]=>
          string(15) "100100000013097"
          ["itemid"]=>
          string(15) "100100000023883"
          ["triggerid"]=>
          string(15) "100100000013630"
          ["function"]=>
          string(4) "diff"

10. Ok, it’s correct, triggers did not change.
11. Sending data to activate triggers once again.

[skuksa@opmon01 zabbix]$ zabbix_sender -z 127.0.0.1 -s TestHost -k TestInt -o 1
info from server: "processed: 1; failed: 0; total: 1; seconds spent: 0.000047"
sent: 1; skipped: 0; total: 1
[skuksa@opmon01 zabbix]$ zabbix_sender -z 127.0.0.1 -s TestHost -k TestStr -o "TestValue2"
info from server: "processed: 1; failed: 0; total: 1; seconds spent: 0.000106"
sent: 1; skipped: 0; total: 1
[skuksa@opmon01 zabbix]$ ./test.sh
      ["name"]=>
      string(8) "TestHost"
          ["itemid"]=>
          string(15) "100100000023884"
          ["name"]=>
          string(7) "TestInt"
          ["key_"]=>
          string(7) "TestInt"
          ["history"]=>
          string(1) "0"
          ["description"]=>
          string(0) ""
          ["lastvalue"]=>
          string(4) "1000"
          ["prevvalue"]=>
          string(1) "1"
          ["itemid"]=>
          string(15) "100100000023883"
          ["name"]=>
          string(7) "TestStr"
          ["key_"]=>
          string(7) "TestStr"
          ["history"]=>
          string(1) "0"
          ["description"]=>
          string(0) ""
          ["lastvalue"]=>
          string(10) "TestValue1"
          ["prevvalue"]=>
          string(10) "TestValue1"
        ["serialno_a"]=>
        string(10) "TestValue2"
        ["tag"]=>
        string(1) "1"

      ["triggerid"]=>
      string(15) "100100000013631"
      ["expression"]=>
      string(20) "{100100000013098}<10"
      ["description"]=>
      string(8) "TestIntT"
      ["value"]=>
      string(1) "0"
      ["priority"]=>
      string(1) "2"
      ["functions"]=>
      array(1) {
          ["functionid"]=>
          string(15) "100100000013098"
          ["itemid"]=>
          string(15) "100100000023884"
          ["triggerid"]=>
          string(15) "100100000013631"
          ["function"]=>
          string(4) "last"
      ["triggerid"]=>
      string(15) "100100000013630"
      ["expression"]=>
      string(19) "{100100000013097}=1"
      ["description"]=>
      string(8) "TestStrT"
      ["value"]=>
      string(1) "0"
      ["priority"]=>
      string(1) "1"
      ["functions"]=>
      array(1) {
          ["functionid"]=>
          string(15) "100100000013097"
          ["itemid"]=>
          string(15) "100100000023883"
          ["triggerid"]=>
          string(15) "100100000013630"
          ["function"]=>
          string(4) "diff"

12. It didn’t work! Inventory have new values data was accepted, but items lastvalues are wrong and triggers did not activated. 
13. Check once again. 

[skuksa@opmon01 zabbix]$ zabbix_sender -z 127.0.0.1 -s TestHost -k TestStr -o "TestValue3"
info from server: "processed: 1; failed: 0; total: 1; seconds spent: 0.000052"
sent: 1; skipped: 0; total: 1
[skuksa@opmon01 zabbix]$ zabbix_sender -z 127.0.0.1 -s TestHost -k TestInt -o 2
info from server: "processed: 1; failed: 0; total: 1; seconds spent: 0.000047"
sent: 1; skipped: 0; total: 1
[skuksa@opmon01 zabbix]$ ./test.sh
      ["name"]=>
      string(8) "TestHost"
          ["itemid"]=>
          string(15) "100100000023884"
          ["name"]=>
          string(7) "TestInt"
          ["key_"]=>
          string(7) "TestInt"
          ["history"]=>
          string(1) "0"
          ["description"]=>
          string(0) ""
          ["lastvalue"]=>
          string(4) "1000"
          ["prevvalue"]=>
          string(1) "1"
          ["itemid"]=>
          string(15) "100100000023883"
          ["name"]=>
          string(7) "TestStr"
          ["key_"]=>
          string(7) "TestStr"
          ["history"]=>
          string(1) "0"
          ["description"]=>
          string(0) ""
          ["lastvalue"]=>
          string(10) "TestValue1"
          ["prevvalue"]=>
          string(10) "TestValue1"
        ["serialno_a"]=>
        string(10) "TestValue3"
        ["tag"]=>
        string(1) "2"

      ["triggerid"]=>
      string(15) "100100000013631"
      ["expression"]=>
      string(20) "{100100000013098}<10"
      ["description"]=>
      string(8) "TestIntT"
      ["value"]=>
      string(1) "0"
      ["priority"]=>
      string(1) "2"
      ["functions"]=>
      array(1) {
          ["functionid"]=>
          string(15) "100100000013098"
          ["itemid"]=>
          string(15) "100100000023884"
          ["triggerid"]=>
          string(15) "100100000013631"
          ["function"]=>
          string(4) "last"
      ["triggerid"]=>
      string(15) "100100000013630"
      ["expression"]=>
      string(19) "{100100000013097}=1"
      ["description"]=>
      string(8) "TestStrT"
      ["value"]=>
      string(1) "0"
      ["priority"]=>
      string(1) "1"
      ["functions"]=>
      array(1) {
          ["functionid"]=>
          string(15) "100100000013097"
          ["itemid"]=>
          string(15) "100100000023883"
          ["triggerid"]=>
          string(15) "100100000013630"
          ["function"]=>
          string(4) "diff"

14. It does not work again. 

There is test.sh script code. 

#!/bin/sh
API=http://X.X.X.X/zabbix/api_jsonrpc.php

AUTH_TOKEN=$( curl -s -i -X POST -H 'Content-Type: application/json-rpc' -d '{
"params": { "user": "test", "password": "test" },
"jsonrpc": "2.0", "method": "user.authenticate", "auth": "", "id": 0
}' $API | grep result | cut -d "\"" -f 8    )

API_TAIL="\"auth\":\"$AUTH_TOKEN\",\"id\":1 }"

HOST_GET='{ "jsonrpc":"2.0", "method":"host.get",
"params":{ "hostids": 100100000010090, "output":"extend", "selectItems": "extend", "selectInventory": ["serialno_a", "tag" ] }, '
curl -s -X POST -H 'Content-Type: application/json-rpc' -d "$HOST_GET $API_TAIL" $API | \
        php -r '$out=fread(STDIN,102400); var_dump(json_decode($out));' | \
        egrep -i -A 1 'itemid|"name"|key_|history|lastvalue|description|triggerid|value"|priority|expression|tag|serialno_a' | \
        grep -v '^--' | \
        cat
echo
TRIG_GET='{ "jsonrpc":"2.0", "method":"trigger.get",
"params":{ "hostids": 100100000010090, "output":"extend", "selectFunctions": "extend" }, '
curl -s -X POST -H 'Content-Type: application/json-rpc' -d "$TRIG_GET $API_TAIL" $API | \
        php -r '$out=fread(STDIN,102400); var_dump(json_decode($out));' | \
        egrep -i -A 1 'itemid|"name"|key_|history|lastvalue|description|triggerid|value"|priority|expression|function' | \
        grep -v '^--' | \
        cat
echo
exit