Did the workshop provide a written description of what they did?
They should have validated that the Camera Control Module, Park Assist Control Module, Body Control Module/Gateway Module and Infotainment Master Controller do not have any fault codes stored and are current in software versions. Any fault codes would indicate a problem to be corrected such as an intermittent break in wiring to the rear hatch. Finally camera calibration should be done.
They may have to reload software to those modules even if nothing is found to ensure there is no internal corruption.
They should have validated that the Camera Control Module, Park Assist Control Module, Body Control Module/Gateway Module and Infotainment Master Controller do not have any fault codes stored and are current in software versions. Any fault codes would indicate a problem to be corrected such as an intermittent break in wiring to the rear hatch. Finally camera calibration should be done.
They may have to reload software to those modules even if nothing is found to ensure there is no internal corruption.