After synchronization is complete your notes supposed to appear in Joplin. If sync was completed and no notes were fetched, either the sync target wasn't set up or the sync target doesn't have the notes.
Please, give sync time to be completed, restart the application and let's see what you've got in the end.
Well, it seems that the number of calls to OneDrive exceeded some kind of limit. I don't know what exactly is going on (and similar support ticket remained without an answer) I suggest waiting for an hour and trying again.
If the error persists you can try moving the data to other cloud, say Dropbox and attempt sync from there.
How many bytes is the backup? Did you save the backup to a synced folder? (A folder such as Dropbox, Or maybe My Documents when synced to Microsoft Cloud)
Answering these questions won’t fix your problem, but I wanted to see what might have caused them and how this might be prevented in the future
As a pure speculation, this backup might have been happening at the exact moment when the computer went to sleep. Even larger speculation that interrupted backup process might have corrupted the profile but at this point it's looks like "wishful" thinking and too many coincidences.
It might be interesting to test this hypothesis though. Many programs are rarely tested in such destructive fashion (at least by their developers). Moreover, such tests are very hard to simulate and automate.