4K Update breaking Multiplayer?

Hi, I just returned to Borderlands 2 after the announcement for 3.
Was farming Terramorphous with a few PUGs for some gear before going into UVHM for a few days. Now I try again after not playing for a few days and suddenly every group I try and join I get disconnected for not having an “upgraded” borderlands 2.

Is the new 4K update messing with Online at all? If so, is it planned at all to get a Linux/Mac Version? Getting frustrated not being able to play with anyone, not even friends online.

Definitely seems to be an issue with the 4K update breaking co-op between Windows and Mac users. Moving you into the relevant category…

Sorry if I posted someplace wrong. First time posting, is there any news of them working on a Linux/Mac update for the 4k?