POE 2 Act 2 Infested Tower Boss Bug

Hi fellow exilers!

I've encountered an interesting bug during fighting the boss of Infested Tower area, I believe it's called Jamanra, the Risen King.
When I was fighting it for the first time I've got owned by the boss, which was quite expected. And I decided to give it a new shot some other day and closed the game via alt+f4. Unfortunately, I don't remember the moment when I left - after I respawned on checkpoint or before that, sorry.
The next day when I logged back in, I spawned right on the checkpoint before the boss (which I think is okay), but the boss was gone, and I could go down on stairs to the next area - I think that is a bug.

It's not severe, but probably somebody can abuse this bug in the future to cheese the bossfight.

Would be happy to answer any questions regarding the case.

Thanks!