Actually, those issues have happened to me.
The few times that the boss stayed invulnerable in my group (I think it was Sabateur’s final boss when fighting Lothar Rendain). We just waited for no more than a minute before he was able to be killed.
Boldur takes a long time to run up the stairs, but runs up after about a minute and a half? (I haven’t sat there with a stopwatch to check)
On Sabateur I normally jump up top on the catwalk above the back end of the room and snipe (if i’m playing marquis or OM/WF) and that works out quite well. But those spawns aren’t a bug or don’t show an incomplete game in any way shape or form. Obviously if your strategy of mobbing everything at the center isn’t working, then change your strategy up.
On topic though, RNG is RNG. I have put 80 hours into the game and have gotten 10 legendaries and I don’t know if that’s lucky or unlucky. If it’s a good ratio of legendaries per hour then I’ll just consider myself lucky, if not? I’m just unlucky.
Gear goes from uncommon to legendary with reduced drop chance the more rare it gets. That’s how it’s supposed to be right?