In most cases, you can solve this problem by clicking on the command button in the Bommer panel that corresponds to the command that launched the window (i.e. the button you clicked to get the window to pop up); clicking on the command button when a window is visible will hide the window.

If this happens with the Bommer notification window, you will need to restart Bommer in order to work around this error.  Click here to read about how to restart Bommer without restarting Fusion 360.

 

This is not caused by any user error.  There is a bug in Fusion 360 where sometimes, the Fusion windows fail to load the content requested of it.  This issue has been reported to Autodesk, and we are working with them on a long term fix.