These are the exact issues we've encountered too. The more the game progresses the worse it gets. My theory is the game maintaining all the data for approval ratings with party members, consequences of decisions from earlier acts, etc. makes performance worse as you go along. I'm afraid of what Act 3 will be like, we're still in Act 2.
We can tolerate the 5-6 second freezing when switching characters, dropped lines of dialogue, 30 seconds freezes when summoning, etc. but the inability to move characters in combat is a game breaker. If Larian could fix that, it would at least allow us to keep playing through the other frustrations. The other issue is most publications aside from IGN have done nothing to highlight this issue, likely because they haven't spent 40+ hours in PS5 split screen gameplay. People should be warned to stay away from PS5 split screen co-op until this is fixed.
As you said, for now we have to consider abandoning a 50hr playthrough until Larian addresses the game breaking bug that prevents players from moving characters in combat.
