We played a multiplayer game in which 2 people created own characters from beginning. The 3rd player joined later and he played Shadwoheart. We then also added Astarion to our party until we found Laezel.
In the camp, we wanted to dismiss Astarion and add Laezel. I did this as host, but when ever I talked to Laezel to add her to the party, I got a black screen. I still heard the background sounds, but was stuck and could not even ESC out of anything. Had to close the game with ALT F4. We tried it several times, also with the second player - it always crashed. I then started the savegame again without letting my friends join, then I could add Laezel to the party, invite my friends and assess her to the 3rd player.
We expect that the game had an issue due to the fact that 2 players had a custom character and one not.