After my post, KDE Komplications, I have noticed some definite improvements in the KDE applications I like to use. I like to use Gwenview image viewer, Krusader file manager, and Konsole terminal emulator. These had all been having problems until I recently installed a new set of updates for Fedora 28. I do not know if this has resolved all of the problems with the KDE desktop but it has definitely resolved all of the problems I was having with those applications. Gwenview no longer crashes and all of the apps now display the correct icons where they showed no icons while the problem existed.
For the time being I intend to continue using the Xfce desktop and the xfce4-terminal because they are fine applications in themselves and give me the features I need and most that I like.
I will probably continue to switch between file managers as I have a different favorite for many of the tasks I do. I like Krusader when I need lots of directories open using both tabs and twin panels. I like XFE because it has a great sidebar that shows the directory tree and makes navigation to distant places easy. I also like the text-based Midnight Commander (mc) for use in terminal sessions. I find Thunar especially good for browsing with thumbnails to locate specific images or documents and it has a good sidebar.
At some point soon I will try the KDE desktop again and see if it still crashes and causes long, resource-eating core dumps.