It may still be a poor connection issue.
Unlike a single-tuner television, the signal from your TV antenna is split between two or four tuners in your Tablo. The device’s in-line amplifier does mitigate the signal loss but channels on the edge of visibility may fall off the ‘digital cliff’.
Moving your TV antenna to a higher location with better line-of-sight can help but switching to a more powerful antenna is a better bet.