Well, if the same happens with other apps too, then it's definitely something to check. Tracking definitely works for me, but I'm using English windows and default visual style. From the look of your app, it seems that you are using DE windows and mainly different visual style, which maybe the cause of your problems? I would suggest to switch UI to default Win 10 UI theme, just to see if it helps with tracking, then switch it back. Eventually, contact directly Ranorex support about it. I guess they will initially suggest all the usual steps, like reinstalling Ranorex (complete uninstall and install). And if nothing helps, they may eventually request a remote session with you
Anyway, even though the tracking is not working for you, the UI elements seems to be available in the snapshot? So the below xpath should succesfully find 'Close' button and your old xpath (with childindexes) should work too.
/form[@controlname='FormFramework']/?/?/button[@accessiblename='Schließen']