There was a similar post about this from Vacaville. It looks like you are closer to Sacramento than San Francisco, and local PBS KVIE forced Comcast to follow Designated Market Area rules and Comcast was required to drop it.
Its 8/21/18 and I want to watch what is advertized "7:00 Downton Abbey" and 8:00 "Miss Marple" why cant I find them.
In my area (TC metro, MN) I can get PBS channels OTA or from linear cable.
It is not unusual for PBS stations to advertize upcoming programs for a sub-channel one or more of their channels. Maybe these programs were being shown on one of the other sub-channels. Was there a special program being shown getting new subscribers?