One of them,
Mahalla, has them all. The other 4, your right, have a broken list.
Is it possible that you list which quest(s) those 4 have in common ?
It must be possible that you find the concerning quest with some direct SQL searching.
Use this :
SELECT * FROM `
roster_quests` WHERE `member_id` = '
xx' ORDER BY 'quest_index' ASC
Replace
roster_ with your prefix and
xx with the id of one of those memebers with a broken list.
Happy hunting