The NPC lady mage at the end of the Coral Heart quest (whose name now escapes me) but the last step is to kill her, returns to 100% health when killed. I thought it might be a spell but interrupt has no effect and I died about 8 times over a couple of days before abandoning the attempt. I did try logging and restarting. Also did allow all the speaking that I could, after combat starts I loose health pretty fast so if they have more speeches to make while fighting I was not able to tell it. it's instant 100% health like when an NPC resets if you get too far away in a fight.

I am on NA PC. I am very new so it's quite possible i am just doing something wrong but I did see another thread referring to it as an old bug, posted there and was told to post here instead.