Very odd. When I go to the instrument picker to pick a trumpet key (in this case F) there are no key options listed (see screenshot) – just an empty space. Yet if I go to Edit Instrument Definitions, they’re all there. How can I get them back?
I don’t have a good answer, but have you tried restarting Dorico? That sometimes clears up little oddities.
Yes, several times. No joy.
If I start a new project, everything is there as usual, so it’s something specific to this file…
In the end I created a new project from scratch (which included all the instrument picker keys as normal) and copied everything over.