I just updated the firmwhere yesterday on an MMM I was running on 5S and then went to 6S for its first test and everything works great. Thats a good one though. I dont know what the firmware would have to do with that wire being burnt.
I know it wasn't a wiring issue as I was running it before I had the firmware updated. I had another ESC and it worked fine, this is not my lucky day for sure.