Looks to me like the solder joint got too hot, melting the solder. There is only three things that will cause that:
1) the solder joint was poorly done to begin with causing higher resistance which caused enough heat to melt the solder
2) your motor was pulling more current than the joint could handle and it melted the solder
3) the wires shorted against something where they are bare on the other side of the connector. I can actually see solder and bare wire between the sleeves and the connector
Either way, I would replace that connector with a new one since it got extremely hot and there's no way to know if it's still good. The fact that the two halves of the connector don't sit flat against each other tells me the plastic was heated up as well, meaning it's garbage. If you replace the connector, it should come with new wire covers but, if not, that is something you should be able to buy at a hardware store. It's just a heat shrink tubing, used all the time for electrical type work and is normally sold in a variety of colors. To replace the tube, you do the following:
1) slide a new piece of tubing over the wire that is longer than what is needed to cover the solder joint and a bit of wire insulation
2) solder the wire to the connector
3) slide the tubing down so that it covers the solder joint, flush against the face of the connector
4) using a heat gun, heat up the tubing until it shrinks down against the wire and solder terminal. Be sure to heat the end against the connector first or it could pull away from the connector as it shrinks, exposing the solder joint like what is shown in your picture above
Last edited by Hydro Junkie; 09-05-2020 at 02:04 PM.