Stepper motor troubles (FIXED)

I know this is an old thread. I remembered it as soon as I just had the issue on my 2015 SO3, upgraded to an XL when that was a new thing.
You can see the black burn mark on the housing where I removed the pin. The other side of the connector showed signs of melting.


So, I knew where to look, and I can put a new connector, but I’d like to know why this happens. Is it simply due to an inconsistent connection, maybe a broken solder joint on the odd choice of connector?
It was clearly hot at the connector. I could feel the heat just holding my hand above the drag chain in that spot.