Lately the coop become very unreliable. We can try multiple puzzles through a session leading to "other player left the game" suddenly or just leaving computer for a minute to discover that board become half empty. Because there is no ability to re-add a person from inside the session so we starting over. It become very frustrating. Sometimes there is also an empty list of users to invite after the glitch. So other person needs to restart the game. Don't know what changed. Both computers are macs