Custom keyboard layout not selectable for most programs

Abstract:

I have copied my custom keyboard layout from my old Macbook to my new Macbook.

However, I cannot select it in the Input menu in the menu bar, except when the front program is Terminal or GVim.

More details:

I have a new Mac, so I copied my custom keyboard layout from the old Macbook to the new one into the folder ~/Library/Keyboard Layouts .

I went into System Preferences / Keyboard / Input sources; I added it using the "+" sign, and it now appears alright in the left bar.

It also appears in the Input menu at the top right , together with the original layout (US) and Emoji viewer, etc.

However, when I am trying to select this keyboard layout, it does not work.

What is funny is that it works only when one of a very few programs is the front program, such as Terminal, GVim, or System Preferences.

Needless to say that it worked perfectly on my old Macbook just a week ago.

Both laptops run under Mojave 10.14.6.

I have the impression that the other programs somehow prevent it , or my selection does not stick.

I searched the internet already for solutions. I came across the following suggestions, all to no avail:

Under System Preferences / Keyboard / Input sources, the option "Automatically switch ..." is off (unchecked).

The file ~/Library//Preferences/com.apple.HIToolbox.plist. has permissions -rw----‒- , so I guess they are fine.

I made the layout using Ukulele many many years, and it has worked fine ever since.

Any hints and suggestions will be highly appreciated.

Best regards, Gabriel