Using latest alpha 3.153. Latest stable Chrome. New 15" MBP 10.14.5.
I have two custom buttons (see screenshot). I use these on Google sheets. They worked fine for weeks until yesterday, when they disappeared and were replaced with the little keyboard icon + caret on the far right.
I added the keyboard shortcut (suggested on old issues) to toggle bettertouchtool. That fixed it.
The problem is, it turns itself off and on constantly. I can use the keyboard shortcut to turn them on, and then 10 seconds later when I try to use it again, its off. Eventually I got tired of using the keyboard shortcut, and then I noticed it was turning itself off AND on without any input.