Diablo not spawning on nightmare

[Genesis2305]

I've been playing Belezebub for a bit. Got to the diablo on nightmare, clear all mobs and guardians on my sorcerer and diablo just won't spawn. His enclosure remains closed.

It's the 6th time in a row I reset and kill everything and diablo just won't spawn. I never had this issue with any characters. It only happens on my sorcerer.

I don't know what causes this and was wondering if others have experienced this / found a fix for it.

[qndel]

there's no fix because nothing is broken, if you can't fight diablo, means you probably missed something - most likely pressure stones you need to trigger