I get that validation warning too but it does not stop me from accessing the web UI.
Note: there are multiple system logfiles. You can move the system media (e.g. SD Card for odroid) to a Windows system and use Linux Reader to read the partitions and files.
- Home-assistant.log
- home-assistant.log.1
- Home-assistant.log.fault
There is this option too:
How to get to your log after restart/restore.
I agree with you that it might be a misbehaving integration. A simple way to troubleshoot a rouge integration is to disable each integration, in what ever order you see fit (one at a time, everything at once then enable each individually, etc.). A more through way is documented here:
2024.5+: Tracking down instability issues caused by integrations.