by Ken Task.
Ok, I lied! One/Two more thoughts ... things to try ...
http(s)://site/admin/tool/health/
no parameters to it ... script just runs. Could be heavy processing so execute during non-prime time if you can.
What it might discover (and has when I've used it) ... issues with question bank. If it can, health will make suggestions (sql commands) one could run via a mysql session with DB.
On several sites I have seen it's recommendations fix things related to questionbank.
Also, there is a cli script called fix_orphaned_question_categories.php one could run.
Run both of those before making the backup to restore, of course.
Ok, now I am out of ideas. ;)
'spirit of sharing', Ken