I'm glad it's working for you, but I did the same thing a few days ago (reset TV to factory settings), and thought it had fixed it, but I turned my TV on today and nothing but a black screen with sound and the menus showing on the TiVo.
Just thought I'd share that because it was working fine for a while but the problem is back.
Same problem here, rare, but annoying bug. Strange thing is you can get to the Sysytem Restart menu, but it won't restart so have to power the box off to restart it, them all is well, until the next time.
Happened to me again this morning. The V6 had been left powered on but set to a channel that was not currently broadcasting (BBC4). Switching to a channel that was broadcasting produced the UI and sound, but no picture for the channel either fullscreen or in the preview box. Fixed by putting the V6 into standby and then back on again.
The V6 stopped in mid programme yesterday - blank screen, orange light, then the multi-language welcome screen. It didn't shift from there until powered off (button at the back) and then on again. No idea if this is related but it's happened a couple of times since I had the box about 6 weeks ago.
And again just now after watching Netflix and returning to Virgin Media. Wondered whether there was an alternative to restarting the box, and discovered that running the Test Formats option in Settings -> Video Output -> Video Output Format restored the picture.
I get the black screen regularly and like VM said plus someone here,you need to reboot. They waiting for a fix. Someone also said to change the HDMI cable,apparently the engineers should have been doing that. I am getting an engineer tomorrow
As I said previously I thought that changing the cable had fixed, but it didn't, it was obviously just working for a bit (by chance).
I end up turning the TV off and on again until the picture appears. Very annoying, my second TiVo box does not do this, but it is only connected to a 1080p display. So is it just 4k users with this problem?