I know this has been reported before but previous posts don’t match or don’t help. Forcing a reload of the NP Template doesn’t crack it, for example.
I’m on a M1 Mac Studio, running in Rosetta mode because of NotePerformer. I attach a cut down score (Pf and Flugelhorn). Only the Flugelhorn appears in the Mixer.
I managed to fix the problem by starting a new project and copy/paste all material but thought I’d report in case it’s a recurring problem…
I’m not at my computer just now, so please confirm that you’re talking about the NotePerformer mixer, not the Dorico mixer. NotePerformer only ever shows one channel in the Dorico mixer (or possibly one channel per instance, if there are multiple NotePerformer instances).
Note that you can use the new NotePerformer (SO) playback template provided by @David_Tee last month to have one instance of NotePerformer per instrument, so you can really use Dorico’s mixer properly.
I’ve used it already in quite some of my scores and am very happy with the ability to control everything from Dorico’s mixer.