All of the above is pure speculation, including my own comments. It may be a simple cable connector that's not fully seated, a defective steering column connection, a defective bus interface at either end, or even a software issue in the transmission controller. It may be something entirely different.
If the BMW techs at your dealership, using BMW's advanced diagnostic hardware and software haven't been able to easily find the problem with access to the car and their diagnostic equipment, there's not a very high probability that the collective speculation of a bunch of guys who have never seen your car will do any better.
Good Luck and do keep us "speculators" informed.
Inside of the ZF GA8HP showing the planetary gears that those paddles ultimately control.