When he freezes I just pick him up and pat him. Seems to work. I have no clue why this happens, and no clue what to do if he were to turn into a burnt husk.
i've only ever found maxwell become charred once, and it was after a mining trip where i kind of had to save scum to get a decent haul so it could've been anything however i have found maxwell become frozen a lot of times, almost consistently when loading into the save