Imac A1347 EMC2840. Burned up M.2 and adapter board. Anyone know a cause?

[Stanl1]

Recently bought this iMac to use. It was described as having an issue restoring the software. At worst I figured the problem would be a bad hard drive. When I received it it would not turn on at all at first. I contacted the seller who basically didn't want anything to do with it. So I decided nothing to lose to open it. Once open I almost immediately noticed that the m.2 is discolored and the bridge that goes to the motherboard was partially cooked. Nothing else seems damaged. I have ordered a replacement m.2 as well as a new bridge adapter to PCIe. Anyone else ever seen this and what could possibly be the cause besides overheating? As I said the unit would not post at all now it does post with the bridge removed!