What is causing the U-Verse channels to freeze despite resetting and diagnosing the receiver?

I've noticed that my U-Verse channels freeze every few minutes. The 'U-Verse Signal Lost' message appears for a couple of minutes before the picture returns, or changing the channel brings the picture back temporarily. My TV is connected directly to the ethernet-wired receiver and gateway, but resetting the gateway and receiver/DVR and unplugging everything and restarting in the proper order hasn't fixed the issue. The receiver's diagnostic says everything is okay, but the options don't match the problem or the error message, so I don't believe the diagnostic system covers this specific issue. This is the first time I've encountered this issue in the time I've had the system."