Intermittent black screen when using Roku Ultra with Samsung TV

OK.  I believe that everything is working now.  I was thinking about what you said about HDR subsampling and wondering why I did not have that screen on my Roku Ultra.  The TV I have certainly had HDR, so howcome no screen on the subsampling.

I discovered that my tv has a way of checking the HDMI cable and signal...so, I though well I'm going to try that and low and behold the check came back saying that I had a bad cable.  Seems rather odd that the cable that checked bad is common to the DTV receiver, the Roku Player and a Bluray player and I had no indication that there was a problem until I installed the Roku Ultra.  Once I swapped out the HDMI cable, everything starting working as advertised and magically the Roku HDR Subsampling setting appeared.  So, it would seem that I never had HDR!  Perhaps the picture will improve now....it has been OK, but not as good as expected.

Anyway, thanks again for your help!  Your suggestions steered me in the right direction.