Repeated disconnects when loading instances (both solo duties and dungeons)

My friend and I are playing on Mateus, and he is getting booted from the server (90002 error) consistently when going into a solo duty or dungeon group, and is then unable to log back on because the server still thinks he is logged in. This happens roughly 50% of the time and it is causing the game to be unplayable. He is playing on a PC and I'm on a PS4. I never get booted off, but the game is effectively unplayable for me as well since we cannot play together.

I've been reading through the forum and have noticed that others are experiencing this to varying degrees (some far worse than us), but most seem to be EU players. We are both NA players on NA servers and the problem is still occurring.

Has anyone found any solution to this problem yet? And SE, can you please tell us what is going on? The expansion came out 3 weeks ago, had a hotfix patch already, and the game is still unplayable for some. This is getting a bit ridiculous now, especially since we are paying money to play this game.