Hello,
Can you please post in what mode is your Firewall profile (public/private) when you have the issue?
Also knowing your OS helps a lot, since there are differences in Firewall on different OSes.
However the best option to pinpoint the issue would be sending us some debug logs.
Please enable debug logging in Settings > Maintenance > Enable debug logging
And complete Firewall logging in FW component settings > Advanced > Log all blocked packets
After setting this, please reproduce the issue and send us the following logs:
"C:\ProgramData\AVAST Software\Avast\log" folder
"C:\ProgramData\AVAST Software\Avast\fw" folder
"C:\ProgramData\AVAST Software\Avast\Fw.db" file
You can then send them zipped to braun@avast.com
Thank you very much,
Filip