Poor connections will lead to more heat on connections. Probably had some corrosion on the metal mating pieces caused the sparking between the two and in no time flat melted. Was this connection thst melted recently plugged back in?
You might be on something. Didn't thought about corrosion but I indeed plugged a connector back in after a fuse breakout.
Also my shack is almost openair and with the temperature difference in winter, it possible that some condensation formed and some corrosion appeared.
I will definitely check plugs more often