I have the mysterious stranger perk. Each time he appears in VATS I get stuck in VATs for about 20seconds after hes has killed an enemy. While any other enemies around are damaging me, my character has died several times due to this.

I did have this happen once or twice, but it didn't happen every time. Definitely seemed to happen with the Mysterious Stranger had to take more than a couple shots to kill the person (because they were behind a barrier or something).