I would have said a CUD error but the fact the "blob" is not morphed in with the rim leaves me scratching my head
sometime canadian site have better input, they call it mortar set, which is Deteriorated Die, or Die Deterioration Doubling
I'm thinking retained cud. the die has broken and shifted but the broken piece has not fallen away and was being held in place by the collar. That's why the rim is still present and it isn't just a featureless blob.