Universal login page taking too much to load through virtual server

Our login window (Auth0) takes more than 20 sec to load. This case works fine on local computer, but doesn’t on our virtual servers, that are used for nightly auto tests execution. So we have many fails in our auto tests when logging in.
This is happening only on dev tenant as dev tenant is on public cloud and test and prod is onprem. So it might be something related to firewall but just wanted to confirm.
It was working fine around 3 months ago.
Any help?