Nahyndri won't die and debuffs and buff timers don't run out

So first of I noticed that some buffs and debuffs last longer than they should, like the enlarge buff, that lasted over a day for some of my characters but not all, with the timer saying something like 19 minutes for hours, the armor reduction debuff from the songbird that lasted longer than the fight and only disappeared after one long rest for Seelah, two long rests for Lan and even longer for my main character. Same goes for Nahyndri, the final boss you meet at the heart. The stuns from the “catapults” last a very long time with the timer beeing stuck on 12 seconds for minutes.

Which brings me to my second problem, Nahyndri won’t die. He’s stuck at 1 hp and no matter what I do, won’t go any lower. I’m assuming the problems are related and that his last stand ability or something similar just won’t run out but I can’t tell for sure.
I’ve been hitting him for over 10 minutes, sometimes while he’s stun locked for most of that time and nothing happens. Then I just sent my characters into a corner to leave him alone for a few minutes… nothing happened.

I’m assuming that my other problem that I posted in another topic, that songbird stuck my main char with the demonic charge ability, is probably the same problem, debuffs not runing out…

Made an account to second this. I think something must have happened during the fight to activate the secret ending. Fortunately I had a hard save right before the battle. Buffs were ok before that point (counting down normaly) but at my first attempt to kill Nahyndri he wouldnt go below 1 HP and i noticed buffs werent counting down anymore.
Not sure if it is related to Songbird, anyway I concentrated on her in my second attempt and killed her pretty much instantly. Buffs were ok after that fight and I could also kill Nahyndri afterwards.