Problem
I was trying to understand what's wrong with my proxies, eg:
1147097:20210327:092134.799 cannot send list of active checks to "192.168.20.31": host [zbx-proxy01] not found
1147091:20210327:092334.832 cannot send list of active checks to "192.168.20.31": host [zbx-proxy01] not found
1147077:20210327:092351.880 sending configuration data to proxy "zbx-proxy01" at "192.168.20.31", datalen 13321203
1147090:20210327:092534.878 cannot send list of active checks to "192.168.20.31": host [zbx-proxy01] not found
1147095:20210327:092648.976 cannot send list of active checks to "192.168.20.31": host [zbx-proxy01] not found

After spending some time i found out what there was configuration issue within zabbix_agentd.conf: both Server and ServerActive were set while only passive agents are used (my bad). Commented ServerActive with #, restarted agent and error messages are gone.

Having in mind mentioned above i propose to do some textual changes in Zabbix error messaging:

Right now we have
cannot send list of active checks to "192.168.20.31": host [zbx-proxy01] not found

Proposed change
cannot send list of active checks to agent at "192.168.20.31": host [zbx-proxy01] not found