Hi Mike C
Thankyou for pointing me in the direction of patching as this is where the issue is.
I had loaded the Factory USB patching from the Library which patched USB inputs 1-24 to Channels 1-24 in order to play back a Multi-channel recording from a USB stick. I then selected playback of a Stereo recording from the same USB stick and found the L/R was playing through Channels 1 and 2 rather than the USB 1/2 channel.
After loading the Factory Local patching the Stereo Playback worked correctly through the USB 1/2 channel. When I looked at the USB tab, inputs 1 and 2 were patched to the USB L/R channel. The same when loading the Factory SLink patching.
In a live situation this issue would not happen because I’d be taking inputs from Local sockets or over SLink and using the USB playback for eg. background music. Lesson learned 🙂