Why my AVAST Automatically pop-up a void window !!!

Recently I update my Avast Free Antivirus program.

However, it begin to pop-up a void window after a while from PC starting!!!

It never happened before!!

However, it can pop-up a void window!!!
What is a void window ?

Post screenshot

I attach the screenshot.

My OS: Win8.1

Is there someone coming to solve it???

Have you blocked AvastUI from accessing the internet?

My PC has been always connecting to Internet.

I have uninstalled newest version, and back to version-17.8.2318. Then, the void window has not come out yet.

Confirmed:
https://forum.avast.com/index.php?topic=212045.msg1436830#msg1436830
https://forum.avast.com/index.php?topic=212045.msg1436977#msg1436977
https://forum.avast.com/index.php?topic=212045.msg1437336#msg1437336

You need to allow AvastUI.exe in your firewall.

Yeah, I’ve already posted this as a workaround:
https://forum.avast.com/index.php?topic=212045.msg1436992#msg1436992
But this is just a temporary fix.
There’s no reason why AvastUI.exe should require an internet connection at all times.
The user interface isn’t supposed to cause any issues just because the user’s computer is offline!

You can submit your feedback in “About Avast”.

Will the pop-up void window problem be solved for next version?

If it will, I can update for the next version. If it won’t, I’ll use version-17.8 all the time.