I had the same problem with my pre-owned certified two weeks after purchasing it, and three mos or so, after that. Each time they had to replace the wiring harness.
The problem is that BMW is using dissimilar metals between the male and female connectors and they corrode each other. When this happens the current has to fight to get to ground and the result of this is "heat". Similar to using aluminum wires on a wall receptacle with copper or brass terminals.
I told the SA this but for some reason the Electrical Engineers at BMW are not getting it.