I’m playing invoker and running gr 45s. consistently, but not constantly, monsters keep getting left at 1 hp and then won’t take damage for about 1/2 a second. I have no idea what could be causing this. Please let me know if more information would be helpful and what you need to address bug.
Edit: Actually, it seems to get triggered by clicking speed pylons.
Blizzard does not answer here. It could be a latency/lag issue if the problem is temporary.
Look at the sticky in Tech Support Forum for Common Connection Issues.
Please read the stickies in this Bug Report section.
Thanks!
I’ve narrowed down the problem after more playing- it’s only happening when the monsters get knocked up due to the Speed Pylon effect. I’ve never noticed this in the past, so I’m fairly certain it’s a new bug. Speed pylons are my favorite. 
I have encountered this especially running 140+ with Tal Rasha’s. It most often happens with the last blue elite. Usually these monsters remain stalled/frozen in place and I just leave them. I treat them like juggernauts and move on.
In the past when I have found a nearby Conduit pylon I have tried to kill the stalled elite. Sometimes they die from the Conduit, but often the conduit kills the elite that the Nemesis and the stalled elite remains. I move on.
Also, to clarify, only by killing all three pack elites do you get the progression globes and the buff to the Bane of the Powerful. So this isn’t about a frozen animation.