This is partially caused by
After upgrade to 4.2.5 if you happen to have a forgotten Zabbix proxy 3.2 or earlier, you will start to get these errors in the log:
This is of course caused by misconfiguration, as different major versions for proxies are not supported. But the error itself is very undescriptive and it's very hard to find the rogue proxy from Zabbix itself, if it's been removed from the frontend. Increasing the debug level can help to guess, where it's coming from, but still doesn't contain an address:
The error is created from src/zabbix_server/trapper/trapper.c line 1166
Please add at least IP address of the host, that sends this data.