Maybe I have an idea what goes wrong:
Duplicati should handle connection interruptions, but after the connection is restored, some cleanup actions could be needed. Partially uploaded files, temporary files and files that are not in sync with the local DB should be detected and cleaned up and fixed. Turning off your computer during a running backup should be allowed, but is not recommended.
Having said that, I guess hiberbation could be a problem in combination with using some particular (or all?) backends. When putting your computer in hibernation, all processes continue after switching on the computer. This may cause conflicts with some or all types of backends.
The connection to the cloud provider probably timed out, so Duplicati has to reconnect and re-authenticate in the middle of an upload. If you shutdown your computer (instead of hibernating), all programs, including Duplicati, will be closed and the backup starts from scratch after powering on your computer.
I guess this could have something to do with the problem that your backup runs forever. After hibernation, connection to the cloud provider is lost while Duplicati is in the middle of an upload and notices that it’s time for a new scheduled backup. The new backup tries to start, but the database is still locked by the previous scheduled run, which will cause the “Database is locked” message.
This this is the most plausible explanation I can think of for problem that the database is locked and no new backup tasks will start.