What does it mean when the screen pixilates every so often?

It doesn’t do it constantly or continually. Does it mean I need a stronger antenna?

And now the tablo cut itself off. It said Playback failed. Unknown error occurred. Is it related?

It is.

The pixelation is indeed caused by a drop in the Over-the-Air signal from your antenna although sometimes it’s also caused by interference.

Breakup of the video and audio signal is the last step before the signal goes away completely which is known as the digital cliff.

Improving your antenna setup can help boost your signal to a point where it’s strong enough to survive occasional dips in signal strength which are super common.