Hello,
Before making any changes to the car, perform a vehicle scan and save it securely so you can always keep track of modifications and revert them if necessary.
See the
VCDS Coding Log; all changes are recorded there. What do you have listed in yours?
I've seen two reverse lights (instead of one) on other vehicles with LED lighting. Did you accidentally switch something over to LEDs somewhere in the lamps?
The LED taillights may have a different wiring configuration.

At least, that's the case with the T6.
Best regards, Rainer.