In a bad sort of way, reliable errors are a good test time.
Viewing the log files of a backup job Complete log will show prior history of "RetryAttempts"
Viewing the Duplicati Server Logs at About → Show log → Live → Retry will show any retries.
Screen 5 (Options) Advanced options –number-of-retries can be increased above its default 5.
The above will help to determine whether the retry exhaustion issue seems to apply in this case.
Alternatively, Release: 2.0.5.104 (canary) 2020-03-25 seems to be holding up well. I’m using it…
The database versions appear compatible with 2.0.5.1, so going back “should” go OK, if desired.
Canary releases are always a bit of an unknown though. Don’t use it on any high-value backups.
This would be just a chance to see if the fix for a retry exhaustion issue fixes this particular issue.