Please check the following:
1.Pull down the device list to refresh the device's status.
2.Make sure your camera is online and the battery has power.
3.If you recently relocated the camera which is not working, check its signal strength; make sure the signal strength is strong in the new location. If it has no signal or weak signal, please try to move the hub closer to the camera.
4.Try to remove the camera from the app and then add it again.