At least with the problems I've encountered recently, it seems both weak signal and pixelation tied back to antenna/reception signal issues.
I'm not entirely convinced something related to signal sensitivity didn't change with the 2.2.18 firmware but the primary issue I was having manifested as visible pixelation, to the point that apparently reception issues resulted in the Tablo rebooting, resulting in several multi-fragment recordings as a result of multiple reboots.
The logs apparently referenced reception/signal issues as the case of the reboots. As a result I upgraded from a Mohu Leaf 50 indoor antenna to a Mohu Air 60 attic/outdoor antenna that I installed in our attic about 2 weeks ago. Thus far, I've encountered no issues with pixelation or reboots during recordings.
So my anecdotal information seems to indicate a recent increased sensitivity to reception/signal issues so you may want to start there.