Hi all, I was having the same issue before, and I have found the fix: update the firmware of your onkyo receiver.
I updated the firmware to the latest version on my TR-626. Now, when I try to open spotify on the Onkyo app, it actually tells me to use the Spotify app instead. So I go to the spotify app, select the Onkyo Receiver under "Devices Available" at the bottom of the app. I am now able to play a track which didn't work before!
This solution is even better, as the Onkyo app worked very slowly and clunky, and there was no random shuffle option. Now, it works incredibly smooth with the Spotify app, and I have shuffle play!