I did some more trouble shooting and believe the problem relates to the player selection.
In Gizmo if you select "Here" in options: "Choose where to play", you get full screen images. Other option is "Player", which also shows controls same as JRemote.
In JRemote, the options for "Available zones" are "Player" and "This device". If you select "This device", which I assume is equivalent to "Here" in Gizmo, it shows at the bottom of the screen "nothing is currently playing" even though the images are queued. If I go back and select "Player" the queue appears. So the issue relates to the "This device" player making the queue unavailable.
Over to you.