[#ZBX-26560] Proxy cannot return to work after long network issue

Steps to reproduce:

Break the network between the Zabbix Server and the Zabbix Proxy for several hours, then restore network connection.

Proxy conf:

Server=10.2.1.81;10.2.1.82
..
DataSenderFrequency=1
..
ProxyBufferMode=hybrid
ProxyConfigFrequency=5
ProxyMemoryBufferSize=10M
ProxyOfflineBuffer=12
..
StatsAllowedIP=127.0.0.1,192.168.1.76
..

Server conf:

SourceIP=10.2.1.81
..
CacheUpdateFrequency=5
..
StartProxyPollers=2
ProxyConfigFrequency=5
..
HANodeName=zabbix-01.exa.com
NodeAddress=10.2.1.81

Result:

Zabbix Server log:

  6890:20250612:043231.570 sending configuration data to proxy "zabbix-proxy-01.ex.com" at "192.168.1.76", datalen 17564, bytes 3579 with compression ratio 4.9
  6989:20250612:073320.906 Proxy "zabbix-proxy-01.ex.com" changed state from online to offline
  6989:20250612:121427.929 Proxy "zabbix-proxy-01.ex.com" changed state from offline to online
  6817:20250612:141630.944 reloading configuration on proxy "zabbix-proxy-01.ex.com"

Many lines like this:
  6864:20250612:144441.302 received id:25897580 is less than last id:26002109

Zabbix Proxy log:

903148:20250612:043231.600 received configuration data from server at "10.2.1.81", datalen 17564
...
903156:20250612:121409.962 Still unable to connect...
903156:20250612:121426.547 Connection restored.
903148:20250612:121430.967 Connection restored.
...
903156:20250612:145534.907 zbx_setproctitle() title:'data sender [sent 6 values in 0.225718 sec, sending data]'
...
903148:20250612:145658.159 received configuration data from server at "10.217.197.81", datalen 36
...903168:20250612:145936.271 zbx_setproctitle() title:'history syncer #1 [processed 22 values in 0.000674 sec, idle 1 sec]'
...
903177:20250612:150041.931 zbx_setproctitle() title:'self-monitoring [processed data in 0.000810 sec, idle 1 sec]'

zabbix[proxy,\{HOST.HOST},delay] item and trigger:
but at the same time:

That is, somehow the proxy and the server exchange information, but it seems that the server does not accept this data.
As a result, there is no new data from hosts behind this proxy.

Expected:
The connection between Zabbix Server and Zabbix Proxy should be restored, old data from the proxy cache and new data should arrive again.

[ZBX-26560] Proxy cannot return to work after long network issue Created: 2025 Jun 12 Updated: 2025 Jun 16
Status:	Open
Project:	ZABBIX BUGS AND ISSUES
Component/s:	Proxy (P), Server (S)
Affects Version/s:	None
Fix Version/s:	None

[ZBX-26560] Proxy cannot return to work after long network issue Created: 2025 Jun 12 Updated: 2025 Jun 16