Tvheadend

When I do 'force scan' for all the TV channels, the 'Status' screen will show it going from one frequency to the next and several of them are 60% to 80%. But then the muxes all show scan status of 'fail' when it finishes. The 'Watch TV' window then offers several local channels whose names I recognize but when trying to play they all say an unknown error occurred. Once I got a few minutes of a Knight Rider re-run that paused every 5 seconds or so, so that was nostalgic and shows the system can probably work.
What should I try to get the the muxes to succeed and show TV?
My local city is listed in the pre-defined networks and the 'Electronic Program Guide' is listing programs. Just the 'Watch TV' does not want to display. I tried on the local host (RPi with latest updates) as well as a Windows 10 laptop.
Thanks for any pointers!