So this temporary protection gain - heal immunity doesn't prevent it, shock doesn't prevent it, and nor does buff immunity. Plague looks like it might work as it damages health directly, except that Enfys also has stacking health steal which could potentially remove it. Sith trooper and assassin might work with their protection bypass attacks, and of course nihilus with Annhilate would trump all, and maybe Fett's execute or vader's culling if you could stack enough status effects or debuffs.
It seems like there was an oversight here, or there's a kit or overhaul coming to counter. But as it is, options to counter seem pretty limited.