If Steam is running: no sessions will show up on same pc coz Steam wont tolerate two copies of a game on same pc
If Steam is running and the games are hosted on two different pc then it will work as expected given that both systems have Steam running.
If Steam is not running then session will show up on the same pc but not on two separate pc unless it’s set to be lan mode
Sessions would not show up on editor because editor hosts it’s own sessions for multiplayer testing, so you need to launch a standalone play during testing
If Steam is running and you enable Steam presence then only the sessions from your Steam region will show up and people outside your region will not be able to see it
If you are testing with appid 480 sometimes the sessions might not show up coz there’s a large no of servers using same appid to test. But this happens very rarely.
That’s all what happened in my experience with Steam sessions so far
You can run virtual machines (virtual box, VMPlayer) and use a different steam id in the virtual machine os and another one in host os. Ubuntu is a good choice since it’s a lighter os and so virtual machines should not have performance issues.
As far as i know there is no way to run two steam users in the same os, or have the game run twice with same steam id (except maybe dedicated servers)
I personally use a old laptop with windows 7 and a separate stream id to test steam connections