Error on adding (custom ) Sharepoint hosted App to a Modern Page

It was working till 25th of May. Now the hosted App present in the modern page returns an error 

But the App is accessible from /_layouts/15/viewlsts.aspx . 

So the app was removed  and installed again , the webpart is now not showing in the Add a Webpart options in the modern page.

Is there any change in the environment causing this?

Thanks&Regards

JAJ