angry bird

I purchased 10 of these camreas and installed at an auto dealership. The image is very unstable, it gets lighter then darker and oscilates. We have noticed it happening more often in bright sunny days. I've been in touch with tech support and they logged into the cameras and shutter speed and the gain and nothing seems to work! They are plugged into several different POE switches, so I don't think it's a power issue. Thanks