The transmission or braking module itself is failing to communicate.

Pull up the passenger-side carpet/sill panel, open the TCM plastic box, and look for water, condensation, or green corrosion on the pins.

Repairing broken CAN bus wires.

I can help identify the most likely culprit and direct you to the specific module to check. VW P1648 Code: Troubleshooting and Solutions | JustAnswer