Delerium simulacrum boss wave bug

While doing the boss waves on wave 12 i killed a random boss that spawned and his corpse seemed to bug out or the encounter ended at the same time he died and it bugged tbh no idea. All i do know i that now when i press the interact to continue waves box by the npc it does nothing and doesn't progress. Bricking the simulacrum and wasting ur materials.

Same problem here. All mobs dead but can't start the next wave. Wave 12/15

Why is this still happening?

Wasting so many shards to this bug.

Happened twice, in wave 11/12 and 14/15.