Channel Scan missing existing channels

I wanted to optimize the list of channels I have on my tablo and remove the ones that I currently don’t watch. I did a channel scan and have significantly less than are currently on my TV. Many of the channels that did not show up in the most recent scan have a very clear picture when I watch live TV.

It could be that these channels are on the other side of a digital cliff - you can learn more about this here.
And you can learn how to solve this here.