Error(s) encountered during statement execution: disk I/O error [QUERY: DELETE FROM fulltextWords WHERE wordID NOT IN (SELECT wordID FROM fulltextItemWords)]
It's not a sync problem — it's a problem with Zotero not being able to write to your database.
Do you have your Zotero data directory on a network share or external drive? If so, move it back to your local disk.
Upgrade Storage
Do you have your Zotero data directory on a network share or external drive? If so, move it back to your local disk.