Damage from monsters occurring after death (post-boss encounter)

After defeating the boss, I remained in the area waiting for loot to drop.
At that point, the encounter was clearly over and there were no active enemies.

However, a delayed rock projectile triggered after the boss had already died and killed my character. As a result, I lost experience despite the fight being completed.

I understand that some encounters include delayed or lingering effects, but taking lethal damage after an enemy or boss is already dead feels unintuitive and unfair from a gameplay perspective—especially when the player is no longer in combat.

I would appreciate it if this behavior could be reviewed, particularly cases where post-death effects can still kill the player after a boss encounter has ended.

Thank you for your time and consideration