Some people have had success getting their 4K boxes working by trying the following:
1. A different HDMI port on their TV. Not all ports are compatible with 4K, etc. Read the operating manual for your TV regarding HDMI ports. It may not necessarily be port 1 - I've seen where it is port 3 for example.
2. Try turning off HDR or UHD or similar adjustments in the TV which seem to cause some of the incompatibility issues.
It is most likely that an issue like this will require a firmware update, possibly on both the Nextbox and your TV, to resolve this issue.
I apologize for any inconvenience.
Seriously this is EXTREMELY POOR SERVICE! This issue was reported in May and we're entering September without a fix. If it's a firmware upgrade that is needed you would think this would be a high priority as more and more of these models will be purchased as the price comes down on them. I feel that Rogers isn't even looking to fix this issue. If I call tech most don't even know about the problem then when they open a ticket it just gets closed with no resolution. I've never experience customer service this poor from Rogers before. Maybe I've been too nice dealing with this and need to escalate this higher. I pay over $400 a month to Rogers I would like to feel I'm at least respected.
I just bought a new Samsung KU6290 4K TV and have been issues with the picture and sound fading in and out for a few seconds. DOesn't happen with apps (Netflix) or Bluray or other devices, just the cable Box. Contacted Samsung and they say it is a cable box problem. Have there been issues with Samsung TVs and Rogers NExtbox 3 PVR? I saw the thread about the Nextbox 4K.