Hello!
Apparently, killing monster is not a conditionto open it. I’ve had a long fight with them (mostly, trolls) several times, and the chest became available while the guardian was still alive.
Steps to reproduce:
Play Chaos Wastes.
Open the chest and get some tough monster.
Take your time.
Here’s the video of me fighting grudge marked rat ogre for quite some time. The chest opened while long before the fight was over:
I’ve faced this bug before Crudge Marks update, and they don’t matter. The video is just one of many examples of it.
What matters is that monster is still alive, but chest becomes available, and that’s kinda opposing to game logic.
Myea I always thought it was a feature as well. Especially early on when wastes was first introduced, bosses seemed to get stuck in random places without you being able to interact with them in any way.
Guess you could say its also a relevant tactic if you face something that is simply too difficulty to kill but easily kitable. Illusionist/invincible fiends have been something I’ve skipped with my party due to how long it takes to kill one.