Showing available rooms to join which have already started

So I have a starting menu scene, and then a main game scene, standard stuff. What I want to do is to allow players to join into the game scene at any time, instead of needing to wait for everyone to join in the menu scene and load in all at once (like in the asteroids demo). I also want to show the currently running rooms in my menu scene. Basically, I want to have the system from the asteroids demo, but I want rooms to stay open to join after the game has started. I know how to do these two things individually, but I have been unable to combine them to work how I want.

I thought it would be as simple as connecting to the master server and a lobby in the menu scene, and then setting up some UI to get the open rooms. Then, in the main scene, I actually create/join the room (as I need to instantiate stuff across the network once I have joined). But it seems that OnRoomListUpdate isn't actually calling in the client connected on the menu when another client creates and joins their room. I'm sure I'm doing this wrong in some way, but not really sure how to do it right. Any help is appreciated, thanks in advance!