Arena reward chest staying locked, not even spawning

I have 1s before the arena quest goes from “collect loot” to “completed” after killing the last ennemies.

The chest stay locked, worse, they don’t even have time to spawn.
Not willing to test anymore as it happend each time i reruned that quest.
Between that and the fact that the last boss is having raid boss health WITHOUT raid boss loot… well, i’ll say no more as it’s not the place but i’ll still think it really hard.
No loot in an H&S is a pretty big problem.