This is probably the digital "Cliff Effect". TV signals fluctuate, and while there was a gradual roll down the signal strength curve with analog TV signal, digital signal degrades to a point rapidly and then falls off the cliff.
Add to that, your Tablo is splitting the signal between its tuners so you are seeing an additional bit of signal loss that could be just enough to knock you out signal wise.
After you've checked your antenna position and aiming to assure that there aren't any obstructions causing you an issue and that you're pointed properly try a few of these things.
- If you're using a splitter between your antenna and Tablo, try removing it and going directly to the Tablo.
- If you're using an indoor antenna, look into a bigger and better antenna.
- If you can, try roof mount.
I went through this with the change of seasons because of my location every year. Spring brings green things and green changed my signal on the back side of the hill away from the towers. Fall dropped the leaves, but what I assume was the warm days and cool nights dorked up my signal and I had to readjust my antenna again.
I've had no signal issues since going roof mount and taking the time to aim it for optimal reception. When the green all sprouted this spring I didn't have to reaim anything.