MM_SUPPIV_MANS1 - Standard Fiori Extension App not loading in extensibility pane in WebIDE

[Advitiya]

We are trying to extend standard fiori app - Manage Supplier Invoice - F0859 - MM_SUPPIV_MANS1 - on SAP Personal WebIDE on our system. Tried to create a new extension project and opened it via Extensibility pane. 
The application screen does not get loaded on extensibility pane and shows a blank blue screen. Only the views/controllers are visible on the right. Screenshot below:

Tried to use refresh button, changed the orientation and also tried different browser, but nothing worked. 

 When tried to extend the controller from here, receiving "Content is not defined" error and unable to proceed. 
Error screenshot:

Console is as attached below for reference

Any help/inputs would be appreciated. 

SAP Web IDE SAP Fiori for SAP S/4HANA  #FioriExtension