In Template Module Interfaces SNMPv2 and similar templates, it seems to be a wrong logic on triiger prototype:

Interface {#IFNAME}({#IFALIAS}): Link down

{$IFCONTROL:"{#IFNAME}"}=1 and ({Template Module Interfaces SNMPv2:net.if.status[ifOperStatus.{#SNMPINDEX}].last()}=2 and {Template Module Interfaces SNMPv2:net.if.status[ifOperStatus.{#SNMPINDEX}].diff()}=1)

Template Module Interfaces SNMPv2:net.if.status[ifOperStatus.{#SNMPINDEX}].diff()}=1

is responsible for the trigger being in problem state only short time when the port status change, it measures the difference between last received and previous value. So problem closes at the next received value, so in default problem lives only 60 seconds even if the interface link still down.

There is thread in the forum about it: https://www.zabbix.com/forum/showthread.php?p=205891#post205891