[Tom Reason]

I’ve discovered the cause of the problem: user error 😐
When I said the PSD file only had the buttons in it I was wrong. When I created the file in Photoshop I used the frame I superimposed over the pictures in premiere as a template to help me position the text. When I saved it just made that layer invisible rather than deleting it, thinking I might want to use it again at some point.
Removing the layer and resaving the file did the trick. Strange since it was set to invisible in Photoshop and I checked that that setting was carried across to Encore.