Custom Apps Integration with Creator App doesn't work properly anymore

Custom Apps Integration with Creator App doesn't work properly anymore

I have a self-developed custom app (Creator app) that I have integrated since a few months via the Setup/Zoho/Custom Apps integration. Additionally I display a related list in a standard module (Deals). Since today it doesn't work anymore. It suddenly throws an error message when I try to configure from the module view: "There are no views in the selected form. Please choose another from to continue.". But I have a form which can be clearly proven as the integration from the Custom App integration in the setup does work! Additionally, when I try to create a new custom app record from the standard module the call doesn't populate the CRM record to my Creator app.  Any ideas?