This issue comes when there is only one user in room in case of 2 User mode.
Can you please share the deatils mentioned below:
1.What is the HOST_NAME you have given in Constant.java file for emulator and device apps.
2.If the server is running on your local system, can you confirm that the server, emulator and device all three are on same network.
3.Can you share your AppConfig.json file which you can locate in the server folder and Constant.java file which you locate in src folder of Client side app.