Hello there, Hunters (and Monsters, too)!
The team is aware of an issue in Evolve on Xbox One where, if a player loses his or her connection to Xbox Live within a lobby, they are unable to rejoin the session through invitation or joining in progress.
At the moment, we are working on a resolution to this, but there is a workaround:
Press the home button (AKA "Xbox button") on your controller.
Select Evolve and press the menu button.
Choose to close the program.
We will update this post when we have more information to report.