yep indeed something that would explain why it fails around a hour. So @MichaIng would need to have a look.
EDIT
as well this might be the reason why V3 is working for me because the upgrade process moved data dir to /var/lib/sonarr and this is protecting the files from being truncated
My goodness, I was never thinking about this. Was indeed a faulty code update by me that didn't include db-wal/db-shm files anymore. Many thanks to all of you for figuring this out. I've fixed it in our code as well: https://github.com/MichaIng/DietPi/pull/3565
I'll additionally ship a MOTD hack, so users should not run into this from a day+ on.