We are using URLSession inside startTunnel() provided by Packet tunnel provider Tested with NWConnection as well - it is also not receiving any response. Response is received only after ondemand is disabled which brings the internet connectivity back. I think there's an issue with onDemand flow itself rather than URLSession / NWConnection. Our 2nd test which mentioned about teams call drops also adds to it (Which doesn't use either of them)

Yes

Packet tunnel provider is caliing some another app which is using URLSession

It's MacOS We are calling some custom extension using Apple's enterprise single sign-on feature. https://developer.apple.com/documentation/authenticationservices

Yes

But in our case, URL Session is calling a public endpoint. That's the reason, it succeeds even when VPN connection is being established. It happens intermittently. Majorly after sleep/wakeup or when enabling onDemand randomly. Scenario that works always: Connect VPN manually. VPN established successfully Disconnect manually. Enable on demand. VPN established successfully automatically. So, I think it's not the same issue as mentioned above.