As of 11/4 PBS Create (Channel 27) and PBS World (Channel 28) are out in East Lansing MI. Punching those numbers in on the remote results in bringing up channel 29. This is not a matter of a loose connection or needing a reset of the box: my daughter who lives half a mile away is having the same experience. VERY hard to get a human being to discuss this with by phone or web.
I doubt you'll get much luck by phone - the decision as to which local channels you get is made locally.
Going by what's on the WKAR website, it looks like a lot of people with Comcast no longer get PBS World or Create (or Kids, for that matter), and the ones that do get them on channels 287 and 288.
Thanks VERY much. After you mentioned that alternative I did vaguely remember seeing alternative channel numbers for Create and World on the channel list at some point in the past. At the moment 287 and 288 are still working for us. Keep my fingers crossed.