Get "...denied" message when more than 5 players try to join world.

We are playing a world that support 8 people but only 5 can play for some stranger reason. When the 6th person tries to enter they get this message. (image) Which says, " thirdPartyConsole.disconnectionscreen..joinDenied unable to connect to world"

If you could help us out it would be appreciated. Thank you for taking the time to look over our issue.