Yeah... the instructions I posted above apply after you clear out all other enemies. This does take several days if soloing them with a fully geared and awakened team. And he appears at least two times in early ch17.

My guild have zero issue with him hes at 18% left currently.
I'm not sure I haven't seen it on my fight against him currently. Maybe its random bug and doesnt affect everyone

when he's alone it is less noticeable, but he heals when he shifts back from avatar state to normal form.

When he's alone it can be countered by silence and a hurok and whatnot.

But there is enough proof that is a bug that is 100% there... it is not random.