Disappearing printers in Mojave

Seems that all the threads I can find have all been closed because of no response or simply no interest shown.

A few weeks ago, my printers and scanners - HP LaserJet Pro M451, HP ink jet 6968 + scan, Dymo 450, Epson scan V370 - quit loading. A restart frequently brought them back. Some time, two or three restarts required. A pain having to open Preferences to verify printers and scanners present. Even if present, a long wait watching the beach ball before the window would open.

I am using Mojave 10.14.6.

Sometime, tried bringing them back by helping - the old Cmd+Opt+P+R. Then that became problematic. As part of my desktop building, when you double-click on the drive icon, the window that opens can be of great use if you drag folders to the sidebar and their address will be bookmarked so you can go back there easily, I have folders such as "T" saved. For example, that will immediately take me to Macintosh HD > private > var > folders > 2_ > (folder with a very long name) > T. Great place to find large install failures of, say, MS updates that did not complete. Direct link to the folder holding the printers and to the Library. Moving a copy of the folder back was no great help.

My printers and scanners were found in my user Library folder. And there were NO printer Apps in my main Library folder. There is a folder containing files for many files for a hundred or so printers for a number of manufacturers. That does not seem to be the issue. Some time ago, I copied the entire printer Apps folder to a desktop folder. Saved me more than once.

When I opened the user > Library > Printers folder this morning, I found that there was a folder for Foxtrot browser developer files. I haven't used Foxtrot in a couple of years. The folder and contents show a modified and Get Info date of 3/13/2019. Folder: CE957A Service Manual Partshere.com_files. I removed the folder and ran Empty Trash. Reboot. Printers appear in Pref window instantly. No delay. No beach ball.

If you continue to have problems, look in any Printers folder for stuff that doesn't belong there. The printer app is what loads. If something is interfering with by being a file that would never load there anyway, the Prefs window may show up - empty.