There doesn't appear to be a definitive answer so far, I was told by the dealership paintshop manager it was likely the applied treatment to the composite panels before primer was applied. Water ingress into the panel from the inside has also been highlighted, the same treatment could be at fault due to a change in colour of the treatment on the inside of newer doors.
If looking for used ensure all recalls have been carried out eg A pillar airbag fasteners, HVAC cover fitted, seatbelts replaced, wiper motors replaced, oil pipes checked for secure fit, brake pads renewed if rust rings show on the discs. Additional problems mine has had/having main screen not working (wires cut when the dash was installed), reversing camera replaced, taillight replaced, irratic startup and idling, difficulty getting into reverse. The paint problem affects early build models, up to mid 2023 I believe, but includes both doors, rear tailgate and both rear quarters, all the same composite material.
I suspect owners who have had all the problems fixed will be able to ask a slight premium as the car will not spend much time at the dealers.