With Windows Defender Application Guard Enabled and Symantec Endpoint Protection (SEP) firewall installed, traffic from network applications (such as the Edge web browser) is blocked.
With Application Guard enabled, network traffic from protected applications is modified in complex ways that the current version of the SEP Firewall does not account for.
Symantec is aware of this issue and will update this document when a solution becomes available. It is not necessary to log a support case on this issue. Please subscribe to this article to be notified of any updates.