Blank Avast Window Showing on desktop

Hi I recently updated my Free Avast AV to the the latest version of the program

Now a couple of times a day I have a blank black Avast window appearing in the middle of my Desktop

The window only contains the Avast logo top left and the close button top right

The window is about 2/3 the size of the normal Avast UI Window

It is no great inconvenience, I am just reporting this in case it is a bug!

https://forum.avast.com/index.php?topic=212319.0