This issue happened to me with one out of two of my Premier boxes. When I ran the same cable drop from the working box to the non-working box, it worked fine, which lead me to believe it was a connection issue and couldn't be a box issue. Turns out the cable drop was bad, although the tech didn't see any indication that it was when using his frequency analyzer. To both of us, once both boxes worked off the working drop, we knew it had to be a bad drop into one of the rooms.
The cable tech replaced the line and the problem was solved. Before that I was losing only certain channels (CBS, Food Network, etc.) or they would record pixelated and stop recording halfway or so. I'm not sure if TiVO tuner sensitivity changed between updates or it's just colder weather, which can impacted fittings and other connection points.
TLDR - This isn't a TiVo problem - This is likely a cable/drop issue in your home where something is bad on the line that doesn't work for certain channel frequencies. Yea, sounds weird, but a drop replacement solved my issue, so I'm sold.
If you have two TiVo's, one of which is working, you can always switch them around to rule out a box issue. That's what I did and that's how I determined it was a cabling issue.