If you’re willing to try what seems like a long shot to me, you could see if list-broken-files sees any problems…
The usual big-gun fix for a database problem is the Recreate button, but I’m hesitating because it can be slow. Perhaps you could say how big your backup is (in source or destination terms) then someone might comment. Actually your post has some BackendStatistics, so maybe this is about 42 GB. That doesn’t seem super large.
Recreate is, I think, more download than upload. That might matter on asymmetric links such as cable modem.
There’s also a question of whether you’d rather keep old versions, or save some space by doing a fresh start.
There are two more expert repairers in this thread. I’m just going to suggest there’s hope for your stated wish.