Hello, We have encountered this problem too (TSI 756181833). We have found multiple domains that cannot properly create WebSockets on Safari and we found that Microsoft Outlook fails to synchronize / connect the Exchange account. Safari displayed errors are exactly the same as above, while Microsoft Outlook logs indicated the following error "Microsoft Outlook: (CFNetwork) CFNetwork SSLHandshake failed (-9810)". This happens while two separate network extensions, one implementing NETransparentProxyProvider and the other one implementing NEDataFilterProvider, NEDNSProxyProvider and NETransparentProxyProvider, run at the same time. We suspect that common includedNetworkRules, as other have described, seems to cause this behavior. Refusing to handle those problematic flows (bypassing the flow in handleNewFlow callback) does not help, it just passes the failure to the owner App, Safari or Microsoft Outlook in our case.