It reported a "synchronization error."
It gave no clue what had caused it.
I tried again, and the same thing happened.
So I viewed the log, and near the end I found this:
Thu Mar 09 16:13:14 2017: Internal error while writing to your Favorites: XmarksException [source: windows, id: 5]: couldn't move file
Well, that gives me a clue! It's probably some sort of Windows permissions issue.
But do you see what's missing from that log entry? The file path/name is missing! Which file couldn't be moved? How can we fix it without knowing what file it is?
Could you please update xmarks to report the actual file (path+name) which can't be moved -- at least first in the log, but then preferably also in the "Synchronization error" message.