The references are displayed fine for me. Have you read this note
for version 3.2.13 (when they added support for Maya 2016 Extension 2)?
Mihnea Balta wrote:Note:
The viewport render engine defaults to "OpenGL - Core Profile" in Maya 2016 Extension 2. Maxwell material previews and some custom draw objects (e.g. grass and sea) do not work with this render engine. To see Maxwell materials and custom objects in the viewport, you need to go to Windows -> Settings/Preferences -> Preferences -> Display and change the "Rendering engine" setting to "OpenGL - Legacy". This compatibility issue will be resolved in a future plug-in update.