Has anyone had trouble joining a game session. I attempted to join and after clicking the green join button nothing. just a dark screen with my mouse curser.
That sounds like the map might be too large for your computer to handle.
I’d suggest talking with your GM about looking at the performance guidelines in the documentation at https://help.astraltabletop.com
Also, make sure that you are not using Internet Explorer, the non Chrome version of Edge, or Safari. They are known to not work.