Can only use custom keyboard layout in certain apps? I'm using a MacBook Pro with MacOS High Sierra version 10.13.2.

I used Ukelele to create a custom keyboard layout. I installed it (using the Ukelele installer), and it works fine in some apps, but not others. I can use it in Chrome and in the Terminal (and I am using it to type this description).

But when I open certain apps, like Mail, Notes, Microsoft Excel, and others, it does not work. When I try to select the layout from the drop-down menu like I would in the other apps, it appears like it does in the others, but when I select it, it does not change.

The keyboard layout I created does not have special characters, it is an english layout (abc...xyz) with most characters in different positions than on QWERTY. It is just an obscure layout, so I had to create it myself.

Any suggestions? I am not as familiar with MacOS, as I am coming over from Linux.
@Tom Gewecke suggested in the comments that I place the layout into /Library/Keyboard Layouts. I did this and restarted, then it worked as expected!

Disabling Siri and having its keyboard shortcut set to NONE (and restarting) did not seem to change it. And I did not have Chinese, Japanese, or Korean keyboards active.