Recently, some players were unable to consistently connect to my game. Whenever the player attempted to connect the server message of:
"Lost connection to cloud server. Player may not be able to join game. Attempting to reconnect..."
Followed a couple seconds later by:
"Connection to cloud server restored."
The game server is running on a M4 Mac mini with OS X and the players with issues are also running OS X. Players running on PCs did not have the issue.
The issue is resolved by going to the server's System Settings: Local Network and switching the Fantasy Grounds entry to on from off.
I have no idea if the setting was ever on in the past or if so, what caused it to turn off, but by making sure it was on resolved the issue.
Hopefully this helps.