Xscreensaver slide show fails after upgrade to 20.04

[MR ZenWiz]

I just upgraded my partner's Dell Inspiron laptop from Xubuntu 18.04
to 20.04.  Before the upgrade, I uninstalled Zoom and Xscreensaver (I
had trouble with them in previous upgrades), and everything seemed to
go really well.

After rebooting into 20.04, I reinstalled Xscreensaver (and removed
xfce4-screensaver because it has been problematic before through this
upgrade and I didn't want to mess with it at all).

There was originally only one image file in her home Pictures
directory, which is where I told Xscreensaver to source the images for
the slideshow, and that image worked just fine.

However, when I copied over images from my machine (also running
Xubuntu 20.04 and having no trouble withXscreensaver and the same
slideshow), Xscreensaver never loads any of the other images.  It's
like it's frozen on that one image.  I renamed the file with a dot at
the front, and now Xscreensaver can't find any images in the
directory, even though it contains 219 other image files that all
display properly from Ristretto.

When I run xscreensaver-demo from the command line, it displays an
error - something about libgnome.so and libglade, but a quick Google
search shows that this error is spurious and does not actually affect
the way xscreensaver runs.

Any suggestions on what to change or set that might make this work?

Thanks.

Mark