I faced a problem (reproducer is attached to FB8918126) when both NEFilterDataProvider and NEProxyTransparentManager matches the same connection.
Safari cannot connect and web socket, other programs (e.g. Adobe Cloud Sync) fail too.
Steps to reproduce:
Enable data filter extension that matches every outgoing connection and returns allowVerdict() it in handleNewFlow.
Enable transparent proxy extension that matches every outgoing connection and returns NO in handleNewFlow (actually, YES and properly redirecting data doesn’t help).
Make sure that both filter data provider and transparent proxy are enabled in network settings.
Open web.whatsapp.com in Safari.
WebSocket network error: OSStatus Error -9810: Internal error
Note that Turning off one of extensions immediately eliminates the issue.
OS is Big Sur beta 11.1