I've been having this issue periodically the past few months. Mobile service had come out to diagnose and update the camera firmware specifically. It seems to have helped at least slightly, as I've only seen the fault appear once since then. I would also occasionally get an error saying the front camera was blocked, but both errors would disappear within about 10 to 15 minutes of driving. If it continues the next step is to send off the car to the nearest service center, as disassembly and possible replacement will be pretty involved.