Sounds like the source of your heat is in the outlet/plug, and the heat got conducted down the wire to the control box. My guess is a loose connection in the outlet, or less likely, the UMC wasn't plugged in all the way, so there was sketchy contact at the outlet/plug interface.Mostly the box in the middle and the plug got hot on the UMC. I monitored the voltage displayed as the current ramped from 0 to 32 and it went from 240 to around 234. I don't think he reset the outlet under load.
You have 6V*32A=192W being dissipated somewhere. Over a long wire run, that's not much heating (when charging I lose ~5 volts in the utility's overhead wires before coming into the main bus bars), but if the bulk of it was concentrated at the outlet connection, it would get pretty hot.