Don't know if this might have anything to do with your problem, but it's worth checking.
Make sure the Auto Park Brake feature is turned OFF in the Uconnect settings.
The electric park brake can be programmed to be applied automatically whenever the vehicle is at a standstill and the automatic transmission is placed in PARK,
Then also be careful not to accidently apply the parking brake during your towing setup routine.
The park brake can be applied even when the ignition switch is OFF but the BRAKE warning lamp will not illuminate, however, it can only be released when the ignition switch is in the ON/RUN position.