I have two Raspberry pi’s set up with volumio, using the app I can log into both Rpi’s (single room), if I try and use the two room configuration the app finds the first device but wont find the second.
Both devices can be controlled via the web UI.
So just me then, its still not working.
EDIT : Well thanks to all of the help on here 
I have sorted the problem. Here’s how I sorted it for future refernce, I thought I had done this but anway.
Fire up one of the devices (Rpi) once its started configure the App (Lan/WiFi, room name etc), once the player starts power of the device. Now power up the next device and configure for the second device (room).
Basically you need to power and configure the first device then shut it down. Power and configure the second device then shut it down. repeat for all devices on the network.
good to see that you were able to help yourself and thanks for posting the solution, I’m sure someone will find it useful!