Can't see Calibre window in Linux GUI

I am unable to see the Calibre window in my GUI. It is running as I can see the Calibre icon in the system tray. When I click on "show/hide main window" I still don't see Calibre on screen but the choice changes in the system tray icon menu.

This is for all of the 3.x releases of Calibre 64 bit Linux. When I revert back to 2.x releases I can see the window/app again.

I am running Ubuntu 16.04.3 LTS