Why is my cable modem going "out of sync" with my provider?

I have a Motorola Surfboard cable modem (new) and Comcast as a high speed provider (because it’s Philly and who else is there?). My internet will go in and out intermittently at some point every day. I called Comcast, and they ran some tests and said their system is reporting the modem is going out of sync. What they couldn’t explain is “why”. Any ideas and/or solutions?