After recent updates and a reboot I seem to have contracted the problems
I was having with the release candidate here:
https://www.reddit.com/r/Qubes/comments/7ygt7d/apps_still_not_launching_from_qubes_menu_in_new/
However, the solution I found last time is not working.
qvm-run -u root -a <TemplateVM> xterm
does nothing. I've tried various TemplateVMs and AppVMs. Dom0 works
fine, but nothing else will open.
I also tried Qubes Settings - refreshing the app list and removing and
adding apps to the menu.
Any other ideas?