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[Canapin (Coin-coin le Canapin)]

There was a similar issue here (with a solution). Perhaps it will give some clues.

No user preferences updating on my site

Users are unable to change their about section in my forum. When they press save it says saved, but refreshing just clears this. Unable to reproduce on Meta. Able to reproduce when I change my bio or change someone else’s. I checked error logs, nothing showing up regarding this. Is there any place where I can begin debugging something like this? I don’t know how long this has been here only after a user reported it today.