I've recently updated the official technic modpack from 8.3.0 to 8.3.1 and already I realize a major difference, as dynamax raid battles have become almost impossible. The AI trainers seem to pick targets at random, attacking each other and my own pokemon much more often than the raid boss. The problem seems to almost fix itself if my pokemon faints, because after that they all start exclusively targeting the boss.
I haven't tested this in singleplayer but it consistently happens in the free Aternos server I'm using.

I am also having the same exact problem.
Sometimes after they KO you, you never respawn. It kind of seems like they zero in on whoever suffers to their supereffective moves.

Thank you for the report, however, this is a dupe.
Original ticket: https://pixelmonmod.com/tracker.php?p=2&t=16596