What does a blank window represent in the list of apps displayed by double-clicking "home"? When I have "Pokemon Go" running, and I double-click the "home" button, I sometimes see a blank window in the list of apps that can be scrolled through by swiping to the right. I've only seen this happen with "Pokemon Go." And, the app functions just fine with, or without it.

What does that blank window represent? 



btw: double-clicking "home" not only shows running apps, but also recently run apps, right?  Yet, I've never seen "Pokemon Go" in the list other than when it is explicitly running (never as a recently run app). So, I'm a little confused.
(Answer added from the comments)

Check the title of the window when you're in multitasking mode.  Some windows are either 'blanked' or 'blackened' in this mode to hide sensitive or proprietary info.  

The window will refresh once it receives focus again.