Close App (from Appdesigner) after crash

While developing a new APP with the Appdesigner I often have the problem, that the APP (or sub-apps) crashes with errors and I'm not able to close the opened windows afterwards.

The close button does not work anymore, in the appdesigner is no sign that something is running, close all, clear all, delete(timerfind) etc. have no effect.

Ctrl+C has also no effect.

Is there anything I can do to close these "lost" windows? So far the only thing I can do is restart matlab.

Thanks for your help

PS: This is just an issue while developing, when unforseen problems appear.