The temp probe issue is a known 3.4 issue (its just a nag and shouldnt cause any issues), I would try rolling back to 3.3, it will solve your temp issue and maybe give a different result on your ATO issue, easy enough to try. @Ranjib can correct me but if you copy your database out and then downgrade to 3.3 you should be able to restore the database and no have to re-create everything, I think that should work for 3.4 -> 3.3.
For looking at the log you want to use journalctl for that, see this link - https://reef-pi.github.io/additional-documentation/troubleshooting/
I will try downgrading this evening. It's odd that the temperature issue just happened today. Been running ok for a while now.