I did everything you suggest. Nothing clears up the problem.
I don't have an external drive connected.
The problem has existed for months. It's not catastrophic but it is annoying.
You seem to be suggesting that the problem is with the hard disk. I can't agree with that. The problem is too specific in that it occurs right after a local commercial on a national feed. Playback is fine and doesn't freeze or show any indication of a problem. It only occurs during live programming and acts as though the pause button had been pressed.