There is a new server-side patch that will be going out in 30 minutes with an important bugfix to monster behaviour which was likely affecting a lot of things in-game. Basically monsters can decide to do a basic attack or a “move” on each “turn”, and they were incorrectly always doing the basic attack even if they did the move. This was causing for example the Lich King to attack you with the sword from any distance, was causing the Musketeer Turret to attack targets it was trying to heal, and probably just generally messing up a lot of boss fights where bosses should have been charging up attacks and instead would start attacking you anyway.
The fix is in place now for fresh dungeon runs and we’re doing a server restart to roll it out to everyone shortly.