Greetings!
I have a list of my server instances, and when player want begin matchmaking, he call Services.Client.GetCurrentGames method for getting list of servers instances. But sometimes he recieved 500 internal error.
I really doesn't know what the issue of such strange behaviour. In most cases it's appears when the lot of server instances registered in playfab multyplayer.
It's cured by termination of game instances by playfab multiplayer dashboard.