The mintmark doesn't appear to be doubled. it's clear the phantom "D" drops off from the mintmark with die scratches.
Does the phantom D look incused below the field or bas-relief above the field? If incused I'm thinking a dropped letter D. To far apart to be a RPM.
Interesting mystery. If incused then maybe dropped letter. But the die scratches? I don't really know. Could also be just a weird lamination or planchet flaw that resembles a D mintmark.
It looks like someone at the mint tried to scratch out the dropped "D", perhaps cocktail hour started early that day?!