Steps to reproduce:

I had some rare events about autoregistration from already added hosts.
Nothing changed on the host side, agent did not restarted, hostmetadata not changed.

Yesterday I occasionally could increase amount of such events.

I've added such config on some linux machines behind 3 of 35 proxy. It returns source IP that is used to connect to proxy. To always have actual ip address on the Host Interface in Zabbix.

UserParameter=soho.hostinterface.ip,/bin/bash -c "ip route get $(getent hosts $(echo "{{ zabbix_proxy }}" | cut -d, -f 1 -) | awk '{ print $1 }') | sed -n 's/.*src \([^\ ]*\).*/\1/p'"
HostInterfaceItem=soho.hostinterface.ip

After that I've got a lot (every couple of minutes) false autoregistration events from OTHER hosts behind the SAME three proxy (mostly Windows). Of course hostmetadata did not change, agent did not restarted.

If I remove configuration above from hosts the stream of false Autoregistration events stops.

It is very odd.

Proxy config

Hostname=zbx-proxy.tubus.local
Server=zabbix.example.com,zabbix2.example.com StatsAllowedIP=127.0.0.1,zabbix.example.com,zabbix2.example.com
LogFile=/var/log/zabbix/zabbix_proxy.log
LogFileSize=0
PidFile=/run/zabbix/zabbix_proxy.pid
SocketDir=/run/zabbix
DBName=/run/zabbix/zabbix_proxy.db
StartPollers=5
StartPollersUnreachable=1
StartODBCPollers=1
StartIPMIPollers=3
StartPingers=5
SNMPTrapperFile=/var/log/snmptrap/snmptrap.log
StartSNMPTrapper=1
HousekeepingFrequency=2
CacheSize=128M
HistoryCacheSize=64M
Timeout=4
FpingLocation=/usr/bin/fping
Fping6Location=/usr/bin/fping6
LogSlowQueries=5000
TLSConnect=cert
TLSCAFile=/usr/local/share/ca-certificates/soho-ca.crt
TLSServerCertIssuer=CN=soho-service CA
TLSCertFile=/etc/zabbix/proxy.cer
TLSKeyFile=/etc/zabbix/proxy.key
#DebugLevel=4
 

Here is piece of debug log from  a proxy grepped by minute 22:30 when i've got a false event from `akcept_ts` host. The configuration `HostInterfaceItem`  was added to `akcept_mail` host.

https://drive.google.com/file/d/14_L3zhOwAbRJqmrqJFwaVVvsvouhoNqP/view?usp=sharing

Result:
A lot of false Autoregistration events

Expected:

Get Autoregistration Events only when HostMetadata or HostInterface really changed on the host.