Couple questions.
Did you place placeable loot in the room with the coffer? Did you place or move a thrall?
I have found that the placeable treasures and placing thralls can also block the purge.
Specifically if the purge can’t draw a line right to the coffer it fails.
So if every angle of access for the coffer is blocked by something, a treasure or thrall, it will not spawn. The treasures you place aren’t destructible so if enough of them block the path the purge fails.
Try rearranging your coffer room and see if that fixes things for you.
It did for me
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