I set up a small test with the same material as you have linked in your second screenshot.
In order to see reflections you will need to add a slight metal value. 0 for the metallic value disables metal. Even though you have a value for the metal channel you are giving it an input of 0.
Here is a few screenshots of a BSP made room with a thin cube for the window to illustrate this. The first screenshot is of your material as you have it set up in your second screenshot.
As you can see there is light picking up value due to the input for your specularity. Note the lack of materials reflected and at this angle this is where I see the light bounce.
This next screenshot is a little closer and with a metallic value of .2
Notice the increased amount of reflected information of both lights and even textures.
This last screenshot is with a metallic value of .8.
Now I have a much clearer reflection of the interior of this scene. This is due to how metallic feature react with lights and the amount of light that is reflected back off the surface.
It could be due to the update itself. Make a copy of your project before testing this. Deleting the Saved, Intermediate, and Derived Data cache from your projects directories will force your project to rebuild when you open it next. This should clear up any unwanted information that has been transferred from an older version of UE4.