Avast Business Antivirus blocking internet access

Like the subject says, the internet connection is lost as soon as Avast Business Antivirus is running on the device.
If I turn Avast off, it works fine. All recent installations were already reverted.

The Device is a XMG P506 Model: P651RE with Windows 10 pro.

The Firewall log of avast is not showing anything that is beeing blocked.

I need some advice what to check next.

See if this helps: https://kb.support.business.avast.com/GetPublicArticle?title=Avast-for-Business-Ports-and-IP-addresses