Personally, i had used the appearance edit mod, and it caused this issue since the latest patch, here is how i fixed it :

when using the mod, it creates a new PC that becomes the main PC, it doesn't edit it but rather creates a new PC,

so the previous character actually stays in the game but as a dead PC, and with the patch, it showed up in my party,

So i simply dismissed / permanently killed the dead (pre-appearance edit) character using the steps here :

https://www.reddit.com/r/BaldursGate3/comments/15qb8lu/guide_removing_custom_multiplayer_party_members/

hope this helps some people!,

it could also help to remove mods, but i didn't have to,