While in Kubuntu, I followed the directions to ...
... and moved the 4 directory out, leaving .config/libreoffice/ empty. I rebooted into Manjaro KDE, and I still don't have an application menu.
Yes, I had reset those before.
In Manjaro, I created a new user "guest". I logged out of my usual desktop, and logged in as guest. This worked! The application menu bar is back.
Unfortunately, this diagnosis now interferes with the way that I work, since the option to use the same /home across multiple distros allows me to work relatively uninterrupted when I hit a bug in one environment that isn't in another.
So, I then logged out of guest, back into my main user ID. From the fix before ...
... I dragged that feature out. Then, starting LibreOffice again, I ran into an error:
Error loading BASIC of document file:///home/daviding/.config/libreoffice/4/user/basic/Standard/script.xlb/:
General input/output error.
I renamed the 4 directory in .config/libreoffice and restarted. The error message is now gone, and the application menu bar is still missing.
So, we're one step ahead in diagnosis, but using the same /home across multiple distros is the way I work. I'm not having an application menu bar problem in anything other than LibreOffice. I've been using LibreOffice in Kubuntu 18.04 for a week. Is this something that is buried in LibreOffice-Fresh? Should I try LibreOffice-Still instead?