The first thing I’d suggest is the same - try running the backup with --no-backend-verification enabled. If the job runs without error, then we’ve verified where the problem is.
(Note that this is NOT a fix as disabling backend-verification means if something goes wrong with a backend file you won’t know about it until you try to restore from it.)
The next thing you might want to do is use --log-file=<path> and --log-level=profiling to create an actual text file log of what Duplicati is doing. If the backend-verification process again seems stuck, check the log file and see what the last few commands here and how long ago they happened.
It’s possible the check is working but going very slowly because of bandwidth or reliability (many failed downloads) issues. Or maybe it’s gotten stuck on something (which would be indicated by a the most recent log entry being many hours old).