Users can't join the existing room.

Options
Sometimes users create new room even though there is a room available.
It often happens on iPhone, 1-2 times in 5 tries. I'm not 100% sure but I haven't seen this on android phones.
This is my source code.
	public void JoinRandomRoom() {
		PhotonNetwork.JoinRandomRoom();
	}

        void OnPhotonRandomJoinFailed() {
		CreateNewRoom();
	}

	void CreateNewRoom() {
		string roomName = "SF" + Random.Range(0, 100000).ToString("D6");
		RoomOptions roomOptions = new RoomOptions();
		roomOptions.IsOpen = true;
		roomOptions.IsVisible = true;
                roomOptions.MaxPlayers = 15;
		roomOptions.PlayerTtl = 5000;
		PhotonNetwork.CreateRoom(roomName, roomOptions, TypedLobby.Default);
	}
I'm using PUN 1.91 and Unity 2019.1.0f2 Personal.
Any advice will be so appreciated. Thanks for reading.