Hello,
I had a bug while fighting with Belial. My crusader was fighting with Belial when suddenly, for no apparent reason, Belial launched a single loop attack. The explosions. And after more than ten rounds of blast attacks and dodging, my hardcore crusader is dead, peace to his soul. If I understood correctly, no way to revive it but hey at least I report the bug.
Regards
I am going to guess that the main fight was longer than a few minutes…
Bosses have an “Enrage” Timer. After a few minutes, they get progressively harder, and spam their attacks more often, and for longer periods.
This is to encourage you to play the game at a more appropriate level for your character.
See: Enrage Timer | Diablo Wiki | Fandom
On Torment Difficulty, Belial has a hard enrage timer of 3 minutes, at which point he will continuously use his Meteor Strike, covering the entire platform at once (impossible to dodge) until combat ends. It is still possible to kill him past this enrage timer (especially with Xephirian Amulet), however, it is very difficult.
This is not a bug.