Boss checkpoint on maps

I understand that if you enter the boss arena and die, it wipes the rest of the progress of the map but tell me why, since I WALKED PAST the checkpoint, and then got stunlock killed by an elite mob, it spawned me at that checkpoint and wiped the entire map. IMO this needs to be looked at. The map wipe should only happen if the boss' health bar shows up on your screen. Also side note, im not sure if it happens to anyone else, but my game will randomly freeze and after about 5-10 seconds, it wipes the fog of war on my map