Undying boss

Hello everyone, I had an issue today, where a boss of the syndicate hideout was literally unkillable, his hp was stuck at ~0.01% and he would just not die, so I decided to teleport out after like 5 mins of hitting him. Mobs outside, however were behaving normally, and even the act 6 boss, the Brine King died normally. So I kept trying to finish the boss until all of the tps were exhausted, but all the efforts were in vain, as the boss just refused to die. So, the question is, whether or not its a bug, or it`s something to be fixed on my side? And whether or not anybody else had similar experience, and how did they deal with it?
Thank you.