We had heard last week that this mob was broken and we pulled it in both instances to check and yes the heal parses were unlike any I have ever seen. It seems when the patch was down to lower the heal components of the three other mobs in the zone, this was absorbed all of that damage output We are seeing heal parses 4x what they already where. It was rumored on discord that their would be a patch today, but I have not seen or heard any mention of it soooooo....
Update will be Thursday and it will include a fix for this encounter for both normal and mythic versions.