My problem is not with some browsers not showing emojis. My problem is with having a "?" char (0x3F) stored in the database instead of an emoji.
Meanwhile I think I was able to trace the source of the issue based on the posts affected. I used a REGEXP_REPLACE query to remove some data from posts, and it seems the REGEXP_REPLACE does not handle some UTF-8 characters properly. Time to try to recover the data from a backup 🙂
