To reproduce, set up a v5.2.0 Zabbix server and Zabbix Agent v5.0.5 with active checks.
I expect the client to connect to the server, retrieve a list of checks and start sending the data.
In reality, I see no data in the server and no error messages in its logs, and following error in the agent log:
I would expect agent v5.0 to continue working with server v5.2. The problem was likely introduced in