You can avoid this error by calling Disconnect Room Server to disconnect from the room server after calling LeaveRoom.
You may experience the following symptom: after starting the game program, the steps to join a room, play a game, and then leave the room work as expected the first time around, but an attempt to join another room afterwards fails with an error “Room connection with id N already exists”. It occurs under a condition that the client tries to connect to a room server, but the channel has been connected to a room server already.
The Leave Room function only makes it so that a client leaves a room. After leaving a room by calling the Leave Room function after the first game is finished, the room server connection is internally kept in the Strix Unreal SDK. If the client directly calls Connect To Room Server in order to join a second room, the error in question occurs. (Using a NodeRoom function instead of explicitly calling Connect To Room Server may cause an attempt to connect to a room server internally and may trigger the same error.)