My XG1v4 box starting doing this exact same thing within the last few weeks. I've had this box for a couple of years now and never had this problem. I believe the hardware is starting to fail. I am planning on returning the XG1v4 to the local xfinity outlet and getting a new one.
My symptoms are not just the HDMI disconnect that the television reports. Often, the XG1v4 quits responding to the remote control. This will last 30-60 seconds before it starts responding again. The XG1v4 user interface is also noticeably sluggish. I've tried restarting and even disconnecting and reconnecting power, but that doesn't permanently cure the misbehavior.
(Note: Dmf2278, the original poster, mentioned that their issue started about three and a half weeks ago. This may be about the same time my issues started. Was there a recent firmware update to the XG1v4?).
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