Visual Studio 2015 - Properties window is blank sometimes?

Just select the empty properties window and press CTRL + S. It will reload.

I have no clue why this works, but it does.

David, I had this problem too in Visual Studio 2015 Community. I found out that it was because my XAML Windows [must the the same for WinForm] was undocked from the main IDE. Once the Designer was docked back inside the main IDE Windows, properties pane was working again.

Same problem in VS 2019 Professional. Properties for projects were displayed, for WinForm controls not.

I closed the form tabs and reopened them. Problem solved.