Perhaps a silly question: could it be that the seat position in the car is saved not only per car but also per race track, and is that as intended? Yesterday, I adjusted the seat position of several cars, but today I'm driving a different race track and all the positions are back to default (on this track).
What cars and what tracks? Probably the issue is that you are actually using "different" cars. For instance low downforce variants are logically a different car than the normal one.
I do not think it is obvious. When I wrote "logically" I was referring to the software implementation internal logic.