Unfortunately, I have no advice on how to fix this, but am dealing with the same issue for at least over a year now. Whatever I am watching on my X1 4K box there is a random flicker. I've confirmed it's the box as well, as my tv apps have no issues, and I've tried multiple hdmi cables, plus previous Xfinity box did not have the issue. I can only assume I need to get a new box, but would love to hear anyone elses input.
What is the name of the HDMI port (embossed in the plastic of the TV)? did you try moving to HDMI 1 or HDMI 2 on the TV to see if the problem changes?
Thanks for the response. I'm actually running my hdmi from the X1 box to a receiver and then out from the receiver into the hdmi (arc) input on my tv. Unfortunately, I was dealing with the issue before this setup when the X1 was connected directly to the tv and using different input. I've already tried different variations bypassing the receiver and using different inputs and cables, but still no luck.
there's the problem. Connect the set top box to the TV's HDMI 1 or HDMI 2 port. then HDMI from ARC (from TV) to HDMI input on the receiver. This will fix any HD 4k UHD etc issues alswo. ARC is 'audio return channel' from TV to sound system.
Appreciate the response once again, but that's not the issue. I'm using the arc input on the TV from the receiver so the tv can return the audio from the apps on the TV back to the receiver. Anyway, as I mentioned, I've already tried bypassing the receiver and hooking up the X1 box directly to other inputs on the TV and the issue still persists.
ARC is for digital audio return to send audio from the TV to the receiver/soundbar. It is not hooked up correctly. Cable box to HDMI 1 or HDMI 2 (check owner's manual for correct one for 4k UHD input).