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
This problem is physics not software,
It is very hard to extract heat from ambient temperatures below minus 20c for any heat pump. The heat pump allows Tesla to extend range but the cost is poor heating in very cold temperatures.
It is impossible to extract heat from cold air, therefore despite the claims Air Source Heatpumps will not work at much below freezing. We have Air to Air heat pumps at home and also in our BMW EV, it's the same for all of these. It's not a Tesla issue but the technology of the heating system being used.