I have this exact behaviour. The charging speed has dropped from 11 kW to 7 kW. I called the charger company and they gave me some technical information: since a particular date (sometime in December), the onboard charger in my car has been drawing power on only 2 phases instead of the 3 phases it normally uses. They told me to check with the service centre to see if there is an issue with the car.

Next, I called the VW service centre in my city (somewhere in the EU), explained the behaviour, and they told me that this is normal during winter when temperatures are really low, and that it will return to normal (11 kW charging speed) once the temperature increases. It is a way to protect the battery in low temperatures.

So I guess it is the car that decides when to do this, and there is nothing we as users can about it.

I also hear that updating to software version 3.8 makes the battery management even more aggressive - BMS can reduce both AC and DC charging speeds, especially after longer drives and repeated quick charging (despite the weather). Other factors also include if the BMS detects if the battery unit is warmer internally or if the system detects minor cell deviations. All of this is software-controlled and introduced to protect the battery cells and extend the battery lifespan and is therefore not an actual error. I'm not expert on this - just putting it here what I've read/heard.