I hope the following description is coherent. 
Recently, the EPG data for PlexTV channels is missing or just weird. PlexTV channels with no Gracenote data have guide cells with just placeholders for the time and the Home cell is empty. A message comes up that says there's nothing available on this channel.
Channel guide cells with Gracenote data are just a solid cell. For these, the guide information is there when I select the Home cell. The schedule is there for at least a week but as mentioned doesn't show up in the guide cell.
Some specific channel names:
The channels with no information at all are in the Gracenote source. Some of the names I'm interested in are Farscape, Classic Doctor Who, BBC Travel and a few others.
The channels with Time placeholders are Documentary+, FilmRise movie channels and Sherlock Holmes.
I've tried changing numbering from Ignore M3U channel number to prefer channel number from M3U.
I also tried restarting the docker image. The version running is ghcr.io/jgomez177/plex-for-channels:5.1.2
I confirmed by watching PlexTV using the PlexTV app that the guide information is there.
One thing I haven't tried yet is to remove and recreate both sources.
If the PlexTV EPG has gone wonky I'll have to accept that. Anyway, thanks for any advice.
Delete and Recreate Database