PoE2 Strongbox Rare Mob is not showing up

I am on a Crypt Map right now with a T10 Waystone. There was a Strongbox i upgraded with Regal Orb and opened. I killed every mob but Strongbox didn't open. It just keeps spamming volatile crags but there is no other mob. I also finished every corner of the map but i am stuck with 1 enemy remaining and it has to be a rare mob, because the map didn't complete. The map overlay also doesn't show me a skull symbol. I am not able to complete my map and also can not complete the strongbox.

Same thing happened to me. Just kept sending volatile crags after me until i left and forgot. Then killed me a screen away.