It’s the amount of users and servers in the room. When you join it on a new server it needs to process and verify the state of the room and agree it with all the servers. As the state is massive in this room it can take a very long time to join it.
If you want to learn more read this: https://matrix.org/docs/older/stateres-v2/
Is there any information of who is making this port? Is it made in house by Firaxis themselves or is this outsourced?
If it is made by Aspyr again I would be very wary of this port…