Poison duration not extendable???

I was trying to beat the chamber of earth. My team is heavy on poison to prevent them from stunning me upon death. But then, one of my poison revenge monsters died, poisoning all enemys. Some of them have been poisoned for a while. And on my next turn (max. 50sec in between), two of them have stopped being poisoned.
This can’t be right!
Devs, can you confirm that it’s on purpose or fix this?

Poison and sleep do not stack only stun as it effects the timer

Yeah if you could stack sleep you could just put a sleep bomb there and spam sleep all forever. Also we may need a new monsters that has Auto-sleep, although it would be very OP.

Auto sleep is to powerful as it shuts down monsters plus with the right Combo you can have monsters asleep forever

Exactly, what if it would actually exist and your front line is Soulstealer, Sleep bomb, Auto sleeper, stun bomb and after that Shadowhunter and Stormloch. Probably almost undefeatable.