Okay, it gets even weirder…
Using FastStone so as to be independent of digiKam, I selected 18 files that were not displaying properly and copied them to a test folder and made that folder a Collection in digiKam.
In Albums View, all 18 images displayed and worked as they should.
In Tags View, even Collections that had been displaying the correct number of items on the blue separator bar, now are only saying and displaying a single item, even when I know there are many more.
In a couple of instances, the blue separator bar would be half-lapped over the thumbnails, either above or below.
Thumbnails that belonged to one collection would be displaying in the wrong collection.
And it gets even weirder…
No matter which tag group any of the 18 test images was displaying in, only a single item would display where there should have been more — and — high-lighting/selecting any of the test images would result in the right-side Tags panel to grey out.
Even weirder still…
I have no idea what was going on in the collections that were out of my view.
That being said, I could see a test image thumbnail and also a thumbnail of the collection above.
There would only be a single item displaying in the above collection.
However, when I clicked on the test image thumbnail, the single thumbnail being displayed in the collection above would change to a different image.
These 18 test images function as they should in other programs that I have tried.