"Source" button missing from Configure Pop-Ups in Map Viewer

[acharko]

I am trying to modify the HTML of a text element that I've added to a pop up in Map Viewer (not map viewer classic). In ArcGIS Online, there is a "Source" button. In Enterprise Portal, this source button appears to be missing. I'm adding some screenshots:

1. ArcGIS Online:

Portal (and the HTML never renders): 

[RyanBohan]

Does anyone know what version of portal is needed to see the Source Button in the New Map Viewer?