The avast firewall should get in before the network shield, why it isn’t is somewhat strange. I have seen this happen with many other firewalls but not with the avast firewall, being integrated I would have thought there would be less chance of the network shield alerting first.

However, we don’t know what your current avast firewall settings are and the one that might make a difference is what Risk Zone you are using; Home, Work or Public.

I can’t be a great deal of practical help as I don’t use the AIS version.