Error After Username Change

[KGodel]

Hello everyone! I'm back!

I run an online clan/gaming community, and up until recently all members were required to have a tag "[zG]" in front of their names. After some changes, we were able to add that automatically (making it significantly easier to use the Member List feature).

I ran a server query to remove the [zG] tags from all usernames in the database (I tested first, it worked as intended). Most of my members are having no issues, but some of them are getting "incorrect password" messages or "account does not exist" when using the new username. On top of that, many users (new and old) are not receiving emails sent by the site, which is a new phenomenon.

Does anyone have any idea what caused this? I have tried manually changing password and the error persists. I have had them clear their cache and cleared the site cache.

Any help is appreciated!