SAP Theme Designer: AJAX Framework Page Preview Not Loading

I am currently working on an SAP Portal which was upgraded to version 7.5 SP04. I am trying to design a new theme with the SAP Theme Designer on the portal. I am able to load the theme editor just fine on the portal. However I am unable to preview the AJAX Framework Page or any of the Framework pages available under Portal Control Previews. I see the popup which tells me "The application preview cannot be loaded".

Below is what I see in the Chrome Developer Console. Everything I am accessing is in the same domain, everything is https so I am not sure why the below error shows up related to iFrames. I am able to load a Fiori Application which runs in the same domain and theme it just fine - but the preview for any framework pages do not work.

I am using the theme designer on the SAP NW Portal (Java Stack) accessible from

Portal Content -> Portal Display Portal Themes ->UI Theme Designer

Portal version information

AJAX-RUNTIME  1000.7.50.4.0.20160613143100 
EP-BASIS      1000.7.50.4.0.20160708110700 
EP-BASIS-API  1000.7.50.4.0.20160613184000 
EP-FLP        1000.7.50.4.0.20160613184000 
EP-RUNTIME    1000.7.50.4.0.20160613184000 
UISAPUI5_JAVA 1000.7.50.4.0.20160713180900

Would appreciate any assistance to help resolve this.