It sounds like the setting for the rear camera has been changed so that Rear Camera Delay is set to ON. To change it follow this information.
Camera System Settings
To access any of the rear view camera
system settings, make the following
selections in the multifunctional display when
the transmission is not in reverse (R):
Main Menu
Settings
Vehicle
Camera Settings
Enhanced Park Aids or Park Pilot
Selectable settings for this feature are ON
and OFF.
The system uses red, yellow and green
highlights that appear on top of the video
image when any of the sensing systems
detect an object.
Rear Camera Delay
Selectable settings for this feature are ON
and The default setting for the rear camera delay
is OFF.
When shifting the transmission out of reverse
(R) and into any gear other than park (P), the
camera image remains in the display until:
• Your vehicle speed sufficiently increases.
• You shift your vehicle into park (P).