My 2015 GMC Yukon XL Denali had the same problem, and it was diagnosed as a bad screen unit, that is what they said, and DeMontrond Buick GMC, in Houston did the repair OUTSIDE warranty for $145.00 and has worked like a charm, 149526 miles now and was done at 87588.... GREAT dealership, 3years ago...
The only problem that I am having now is that the rear never did play through the Bose sound system, still cant figure it out... It plays the DVD in the from and sound from all the speakers, but if I use the RES for USB, it will not have any sound, but was told that I needed a different headphone for this system, but I think that there is only wired, and NOT wireless capability?
I only have one remote to use for both screens..., also you can adjust the screen brightness with the remote for the rear screens and that made a world of difference for the screen, but still no luck with the wireless headphones..
Thanks
Judd