Sometimes connect to photon server but nobody inside

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Normally, I set room will start when two players in a room, and max player is set to two, too. However, sometimes when I debug, click connect and everything go right(load scene, etc..), but only one player in a room. I set two player in a room will start to load scene and play, but strangely only one player in a room and start loading scene. How to fix this problem, thanks. I need the room has exactly two player .