I think the problem has been fixed by Texstar (or Joble). This afternoon
xfce4-taskmanager was updated from ver. 1.0.0-1 to 1.0.0-2. I just updated, and the newest version is behaving normally.
The utility has also returned to the menu structure: it's under
PC [main menu] >
More Applications >
Monitoring >
XFCE Task Manager. I'm attaching a screenshot of its output.
A big "Thank you!" to whoever did this. If it was you, Tex, you are The Fastest Packager in The West. If it was you, Joble, you're ... well, The Fastest Packager in Montana.

Thanks again; it's great to have the Task Manager working.