When using proxy on localhost teams fails to establish TCP connection for login

Dinesh-MSFTthanks for the answer! I still think it would be good for the Microsoft Teams Dev team to evaluate what's going on in teams when connecting to a proxy on local host.

What we are experiencing it not expected behavior, and it only happens on Windows when connecting to a proxy on localhost. We tested with multiple proxies and of course we made sure that the proxies are configured correctly, so that traffic is not blocked from the proxy side.

I posted a lengthy question that includes Wireshark traces on stackoverflow as well: https://stackoverflow.com/questions/78509456/windows-10-11-connection-to-localhost-proxy-fails-on-tcp-handshake

What we see is, that Teams sends different SYN packages when connecting to localhost -I don't think this is expected behaviour!

I read through Microsoft's recommendation for proxy servers - but to be frank - they are not very helpful for getting to the bottom of the specific problem we found. It would be great if we could connect to someone from the Microsoft Teams dev team to discuss our findings in depth. If there is a better place to raise this ticket please let me know.