I shot him 22 health units, lost, and after the progress was lost and again became 263 health units 
Has happened twice to me. First time I had Aegis of Death got him to ~60 and lost and he reset to 60. 2nd time nothing special got him to ~120 and he reset.
Got the same problem three times in a row. Got him to ~50, ~100, ~220, but this little bastard always resets to 300 hp. For what iāve payed money, little indie company? 
Same issue here as well, i fought the Boss twice. His Health always reset back to 300 no matter how much damage i deal.
Same.
First time I got him down to around 45 hp, came back to him and he restored to 300hp. Got him down to around 150 again, and now he is back at 300.
Will try to one-shot him, luckily his abilities are not that powerfull.
I here to say me too ā¦ got him down to 76 and when I went back inā¦back to 300 ā¦ Iām having more problem getting past f-ing Ozara more than onceā¦heās an @sshole!
same issue here, but this has to be a thing from today, because yesterday I got mine down to 192 on a āfailedā heroic run, but today heās stuck there.
this also applies to the āHearthstoneā treasure btw, so if you use that he will reset as well.
There was also another bug yesterday where after I used āHearthstoneā to return to the tavern and reengaged the bossā¦and he just kinda blew up. Granted he was at 12 HP remaining, but I actually wanted to bring him to 1 to finish him off with Finleyā¦instead he just got damaged byā¦something? on turn 1? Maybe this is somehow related.
Same issue. Heroic run on 2nd plague lord. He was at 65 health. Got to him with 2 hearthstones. Thought since health is persistent i would easily be able to whittle away his little remaining hp escaping to the tavern twice. Got him down to 47 on first try and used hearthstone. Go back to fight after tavern and he is at 65 health again. Thought maybe when using hearthstone it resets him to the health from the current run. But after dying on my third attempt he had 31 health remaining. Got back to the selection screen he is at 65 health stillā¦
Same here, fought the 2nd boss the third time a few minutes ago. He gets stucked at 267 health. Really annoying. Had him down to 32 alreadyā¦
Same here, murloc boss was fine but all of my runs on Kāzrath he resets back to 300 afterwards.
Same here, murloc boss was fine, Kāzrath keeps recovering to full after each run. Got him down to 150-120 each time.
To everyone in this topic: the issue is known. See Small Client Update: 15.2.2
Blizzard is working on it, but has not given as estimate when it will be fixed.
2 Likes
Same here, on EU server.
I beat Murloc boss to 40 health on heroic, lost, and then in the start menu he had 156 health left.
So annoying.
Latest patch seems to have fixed the issue for me: now all Plague Lords retain the proper amount of HP. Lady Luck has been on my side to make up for some lost time: Iāve defeated the Death Plague on my first run! 
I had the opposite happen. The plague lord gained life during the run, but when I went to play him again ,he was down 10 less health.
The adventure saves the lowest health value the Plague Lord had during the game, not necessarily the one it ended the game with. This is intentional.