Got also a M3 LR and never had any battery heating probles with it. It's the opposite, when I'm travelling and I need to use the supercharging stations it preconditions the cells (warming them up) just before I get to the station, so charging is faster.
Also, Tesla's 21700 cells have a different chemistry and design than the regular 21700. Small details made by Tesla + Panasonic.
How many miles do you have on yours so far? I got 12k miles on mine, same model as yours, and battery degradation is zero!