Well, another experiment failed.
To see whether the problem carried over to Linux, I installed Linux Mint 19 Cinnamon, got the initial ticks worked out of that, and installed digiKam 5.6.0.
I have only gotten a very few of my pictures initiated into the Linux digiKam and I have all the same problems that I was having in Windows plus several new ones.
One of the weirdest is that, when I am in Tags View and click on a tag to view all images that carry that tag, the thumbnails keep swapping places as I mouse over them; for instance, a thumbnail with a red truck will become a thumbnail with a green car.
Plus, in Linux, images that don’t even have a given tag and never did will show up in a tag search.
My workflow has been the same for ages.
I use DIM (Digital Image Mover) to rename/renumber from the SD-card into my dated folder structure.
I then use DxO to enhance and convert the RAW files into jpegs.
I then use FastStone to add Title, Subject, Lens info, Flash info, and Comments.
Once all of this is done, I use mostly Photoshop Elements 7 to do the beginning and end of the editing, supplementing that with GIMP and various other programs when needed with all of this work being incorporated as layers in the Elements layer stack.
I save the finished product as a jpeg which I then and only then admit into digiKam.
The only operations I do in digiKam are to add geolocation information and keyword tags.
Once through digiKam, these images remain in that same folder; they are considered finished and it is very seldom that any other manipulations would ever be done to those particular files.
Yet, when I use digiKam to try and find all images carrying a certain tag, it is anyone’s guess as to what I will get and I cannot and do not trust the accuracy of a simple tag search.
The more I think about it, the more I believe that all of these problems followed upon the heels of me updating digiKam from a somewhat old version to what was the most recent at that time.