I don't normally bother looking in here, being mostly into small scale and windy boats, but the headline caught my eye.
https://oscarliang.com/choosing-gold...ors-motor-esc/ might have some good clues. If it isn't the actual connection causing the problem, it could be wire that is not quite heavy enough for the current causing heating. Thats how fuses work - a bit of thinner wire than the rest of the circuit gets too hot and melts, which is generally a good thing. But if it is insulated wire that is supposed to be kept separate from other wires, its bad news f the insulation melts.