Invisible Mobs in "The Creeper Candle Conspiracy"

In Minecraft Dungeons II, some mobs are invisible (in the quest called "The creeper candle conspiracy") at the location where the second candle has been placed, the invisible mobs do damage and cannot be attacked. Tho mobs have shadows and arrows get stuck in them, but they cannot take damage. Even after I die, the invisible mobs are still there. If I reset the quest, the invisible mobs are still there.