I have a previous model TV but maybe can help.
When this happens, if you go into the TVs menu for Cablecard and look at the CableCard Status and Conditional Access menus to see that the TV does see the cablecard. If it does, then the problem may be the Cablecard itself losing it's authentication for the cable network. Do you get any messages when this happens?
By unplugging the TV you're forcing the CableCard to perform a power-up authentication with the cable network. I would call the cable company and verify that they have you properly configured.
Also, who's your cable provider and which market. I'm working with Toshiba on a problem on my set where every few weeks many channels become corrupt due to an apparent tuner issue but appears to be caused by the cable network. They've confirmed that other markets are seeing the same issue and believe the cable network is passing incorrect info to the TV during occasional network updates.
Toshiba 62MX195 1080p DLP w/ Cablecard
Comcast Cable of New England