I find the same issue with my local ABC channel. I think it is the channel itself and not the Tablo/Roku. Quite often it is intermittent like you say, but then goes away from long periods of time. it happens mostly with General Hospital and my wife screams at me because she ten has to wait a day to watch on HULU with commercials.LOL
A/V sync issues have been around for awhile, even on Legacy. I have had it happen a few times. It’s not the station. I had multiple recordings in a row. The overlap of end of one to the beginning of the next was fine, but when I went to play the actual recording for the next, it was messed up.
From what I have read, Tablo tends to use lots of short files instead of one big one for the recording. It seems as if some master file or other gets out of whack, the whole thing is messed up.