Missing (at least) channels 800-899 on 1 tv (out of three), why?

Just returned from house sitting for 3 months, finding my bedroom tv no longer has channels 800-899 on it. But the other 2 tvs in the house do have them. Did a "System Refresh" with the Chatbot, but I'm still missing them on that tv. Chatbot useless after that. Unplugged, replugged, still no. Was working fine when I left on Oct. 30. Why are they missing only on one tv?