So guys, we probably will have to fix it ourselves, since Blizzard, honestly, doesn’t care.
What I did yesterday was getting someone who had the achievment Awakened Flames link me the achiev in game chat, then checking which boss was marked as not completed. Then I proceeded killing that boss even if I wouldnt get loot just to see if the tracking issue would be solved, and it DID.
By killing the remaning untracked bosses from the achievement fixed the problem for me. Best of luck to all of you who want your title in pugging those untracked killed bosses.