I know what you mean. I experienced it a couple of times. It’s like he will start casting but then just stands there. I also did the quick tap and hold variations. It comes and goes.
I’ve also experienced this. Sterilize seems to be somehow broken. Most of the time doesn’t respond to the activation command, and I’ve never noticed any healing coming from it, no matter how many effects I cleanse.
I would even risk to say that sometimes it doesn’t even increase HP at all, but that may be just me being mad at the skill for how badly it works