yep indeed something that would explain why it fails around a hour. So MichaIng would need to have a look.
[hr]
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
Unpacking sonarr (3.0.3) ...
Setting up sonarr (3.0.3) ...
Found NzbDrone database in /mnt/dietpi_userdata/sonarr, copying to /var/lib/sonarr.
Yes, a hot fix would indeed be nice. 
Here’s what I’m running with mono 5.20 now that’s had me up and running since yesterday:
nano /boot/dietpi/func/dietpi-logclear
- Ctrl+W, type ‘.db’ enter. You should see an if statement containing *’.db’, append * to it like ‘.db’.
- Save: Ctrl+X, Y enter
All working fine now thanks to Taloth detective work.
I’ve restored my original backup so all back to normal now.
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.
Just to copy the Quick Fix from GitHub for the once who did not have MOTD activated.
Quick fix:
sed -i "s/\*'\.db' /*'.db'* /" /boot/dietpi/func/dietpi-logclear