The one that works was a fresh install of the 21.1 plugin, the one that doesn’t work was an upgrade.
You have then to download and install (after removing the current version) a fresh version from the home page (or top level menu). The version from the update is not up to date with all the test domain patterns.
I made some progress. The license message is correct now, but the site still becomes un-responsive. I will try using xdebug on it tomorrow to see if I can figure out where it is looping. Thx again for your help.