The 7.0.2 version has a very buggy editor. By clicking on some groups it crashes with a 100% certainty. Oddly enough, one of the affected groups was the built-in “Switchers” group. I suspected a corruption by syncing to and from dropbox, so I’ve switched the sync off and removed the affected groups in the Keyboard Maestro Macros.plist
But it seems to be a more generic issue with the editor: by creating a new macro and trying to select a keyboard layout in the “Set keyboard layout action” KM crashes instantly. Summing up, the most recent update seems to introduce some very serious bugs.