Think the issue is one device is playing the music through the streamer, and the other is having the music playing on the streamer and using the device to control it.
There is a huge difference between Tidal on a phone, and Tidal Connect on my streamer. The way to test is play music, then close the app on the device, if the music stops you are playing music from the device and not streamer. Another way is that when the streamer is playing, you should be able to control it from any device, more then one at a time.