Ritual Encounter Broken. No mob to kill. Wouldnt let me complete. Had to abandon map

What a frustrating event. Inside the ritual encounter that wont end unless you eliminate all the mobs with no last mob to kill despite laying down an AOE spell on every nook and crannie and corner within the ritual circle. I eventually had the idea to just let it kill me so I could complete the map and not go near the ritual since it was a juiced T16 with high rarity and I hadnt collected anything, and after I did let it kill me, the checkpoint was so close if spawned me right back inside the ritual encounter to which I could not end because there were no mobs to kill. Only constant purple orbs from plants to constantly dodge while trying to find the mob that was not there. Absolute crap having to abandon such a good map for no good reason other than game mechanics.