The per-backup log is in ~/.config/Duplicati in a file with a random name, and.sqlite at the end.
This is a per-backup database file that also tracks the remote contents sort of like local cache.
Its path is in the Database tab of the backup, if you ever need to figure out which DB is which.
There’s a Recreate button if the DB breaks and it needs to be rebuilt from remote file contents.
This unfortunately loses log, right when one might want it for debug… One can manually copy.
The Duplicati-server.sqlite has all the backups’ settings and some statistics but not tiny details.
There is actually also a bit of logging in this DB, but it’s the About → Show log → Stored one.
What Duplicati version is this? 2.0.5.1 has updated Amazon dll versions, and it might matter…
‘Amazon.AWSConfigs’ type initializer threw an exception
solved that similar-sounding problem somehow. Perhaps @Thales_Queiroz can offer details.
Or maybe (like yours) enough fiddling eventually made it behave for reasons that aren’t clear.