Hi @Clive_Pinder,
My apologies for your post having fallen through the cracks here.
Unfortunately, the response will be anti-climactic.
Here is my understanding of why:
The Chord Mojo does not expose its volume controls to Roon via USB which is a known limitation of the device. This means fixed mode is the only option.
The puzzling part is the part where you mentioned it worked before. How has the configuration changed if at all since then?
Regards,
Wes