NAD M17v2i and U-verse Compatibility Issues

I've tried several of the U-verse boxes of different models and ages to feed our programming signal into our new NAD M17v2i surround processor and we get a blinking of our video feed on screen with all of them.  The blinking is intermittent.  Sometimes several minutes go by before a blink will occur, sometimes there may be several blinks within a short time.  Lengths of signal cutout can last from a very short blip to one that last several seconds.  My NAD Processor list that the signal being sent by U-verse is 4:4:4 color space rather than what I expected to be 4:2:2 since signal is 1080 HD being rather than 4K being fed from the box.

Has anyone else experienced something similar?  Does anyone have any suggestions for possible solutions to the problem?  Thanks in advance.

PS I'm stuck using U-verse as long as my wife's parents are living with us as it is the only local provider for the sports channels they watch for our local teams.