cannot be thrown into the P position

It's a 2014 CLA, do you know if the current battery is fairly new? When was the last time it was replaced? AGM batteries do last longer than stanard non-AGM batteries. If it's more than 5 years old, I would replace it and it might just help fix this issue and some other electronic gremlins. Current Mercedes electronic systems are somewhat sensitive to the presence of an optimum charge level in the battery.

the battery is not new, otherwise I will try it, thanks for the advice so far and I will let you know how it turned out