Ah. Yeah, that sounds like Keyboard Maestro and/or Keyboard Maestro Engine don't have the permissions they need from macOS.
Check System Preferences » Security & Privacy » Privacy » Accessibility:
and make sure that Keyboard Maestro.app and Keyboard Maestro Engine.app are both listed and checked.
If they are, try un - checking them and then re - check them. Because sometimes macOS is a dumb ox.