Hmm, I think something is actually going wrong with the Foundry server when the last person joins and it’s displaying the license page as a fallback of some kind.
Have a look here at your Foundry server’s debug logs for the last entries before the error happens. There’s likely some kind of error being logged there that would explain what’s going on.
I’d also recommend trying to replicate it in Safe Configuration to eliminate possible package errors.
Please let us know if you manage to find the cause after trying these, or else you might need to create a ticket in the #ticket-support channel of our Discord server, where you can post an invite to the game to have one of us hop in with you and troubleshoot it from the inside.