One possible cause of this is having images embedded in your notes, which isn't officially supported and won't sync. Usually that results in a different error, but if they're big enough the sync can just fail.
Searching for <img in All Fields & Tags mode can help you find any notes with images.
If you don't think it's that, we'd want to see a Debug ID (different from a Report ID) for a sync that fails.
Searching for
<img
in All Fields & Tags mode can help you find any notes with images.If you don't think it's that, we'd want to see a Debug ID (different from a Report ID) for a sync that fails.