I had this issue. I found out one of my ram sticks was corrupted. I took out the bad ram stick and I never got the issue again. I recommend looking up how to do a memtest to see if your ram is corrupted.
Infernus Ult is completely uninterruptable by anything in the game other than killing him. This is also true for Warden but only once he has fully finished the channelling part at the beginning of it.
