Our guild has reached last boss Caldoran in Scarlet Enclave raid, and faced the bug that makes this boss unkillable.
We did 10 pulls and realized that every time boss HP restored to full, no matter what we do.
Basically after killing the [Scarlet Martyr] ads they keep casting the 10 second [Devoted Offering] spell, which heals the boss.
We tried different tactics and methods to avoid it but with no success.
You can check the sequence of events from warcraftlogs link, since this is the only source we can provide: (you can check other pulls also, it was the same)
warcraftlogs reports #NR41xtFT9c27JWBP
It also names one of the mobs as Pile of Ash - but i suppose it is just warcraftlogs visualization.
Events (pull 9):
00:51.215 Death [Backstab] Backstab Rogueliam → Scarlet Martyr 2
00:57.498 Death [Melee] Melee Vithrill → Pile of Ash 1
01:01.233 Cast [Devoted Offering] Devoted Offering Scarlet Martyr 2
01:01.234 Scarlet Martyr 2 Devoted Offering Grand Crusader Caldoran +2656382
Hope we it can be hotfixed as soon as possible.