It seems to be running fine now, I've quickly loaded the game to see if anything had changed and swapping characters is not freezing the game at all and the summons are instantaneous without any kind of lag, gotta check how the game runs during combat.
What I find weird is that Larian has not addressed this issue directly in the patch notes, just some optimization notes that they improved performance to reach FPS. But well, I'm happy that is running great again, finally I can get back to play the game.
That's good to hear! I mean, they did mention they optimized a few things on the patch notes and that might be related to our couch co-op issues! Unfortunately we're past the worst in Act 3 so I am looking forward at seeing other confirming the issue got better.
We’re about 30ish hours still in Act 1 (where the lag/freezing was unbearable before) and had zero lag or freezing when summoning when we used to have 10-15 second freeze 0fps. Havent had a chance to test further than that yet, but seems to be fixed on first look!