From Tim at Tablo support: “Can you try running another channel scan but this time, make sure you hit the “Add to Guide” button on your screen when the Tablo channel scan finishes? This will ensure the frequency change is saved to the Tablo database, which in turn ensures the Tablo isn’t trying to access the old, empty frequency.”
This worked for me after I removed my distribution amp to stabilize my signal.
I have a Cm-7777 preamp with a 4 port distrubution amp. I removed the distribution amp before Tim’s suggestion worked, but the “Add to Guide” after the rescan seemed to work for me. I had tried the adding the rescanned channels to the guide previously with out results but tring it again after removing the preamp, I did the “Add to Guide” and having been receiving WFAA ever since then.
I also had to reorient my antenna. Since I have a multi path situation that was tricky.
Hey Nell0214…
Turns out my problem was an old Radio Shack amplifier (I know I’ve had it for over 20 years) that I had been using. It has gotten really hot here (North Texas) in the last couple of weeks and I think that the heat finally got to it. Mounted in my attic.
I replaced it with one left over from TWC/Spectrum that was lying on the floor in the attic and service was restored.
Yes, I already did a rescan and add channels. That was the first thing I tried, several times.
FYI, a couple of weeks ago, the local NBC DFW (channel 5.1 and 5.2-COZI-TV) affiliate changed frequencies and I lost it. Contacted TABLO support and they gave me the same advice almost word for word. 
Same thing here. I did the rescan and add channels several times at the start, but I did not always do the add channels after suseqent rescans because I did not realize its importantce.
Not only did the frequency change but some other things about the signal changed also. I tweaked my system for 2 days before I managed to stablize the signal enough to start receiving the channel again. So far I have had no problems since the 3rd day after the repack. I feel like everything is a balancing act now. I hope the other channels in the repack do not present simuliar issues. I can not go bigger and higher.
Receiving the new signal was never a problem when the antenna was plugged directly to the tv after I rescaned the tv.