Hi Raimund,
If you move a microflow or page between modules, you have to re-select which roles can access this microflow or page. This is because the module roles can be different. You can re-select the role in the properties of your page/microflow (right click in the flow/page → properties). The roles might already be selected if they are called the same. In that case just go to allowed roles in the properties, check whether everything is alright and hit ok.
Hope this helps!