This new software update for the Tesla Model 3 and Model Y apparently initiates the recalibration of a vital component of the heat pump, which may have caused some defects and the failure of the entire heating system in very cold winter temperatures.
https://www.notebookcheck.net/Tesla-tries-to-fix-the-Model-3-and-Model-Y-heat-pump-issues-in-cold-weather-with-yet-another-software-update.593406.0.html