I can't see an instrument staff but the instrument shows up in players

I have two guitars in my players, but I can’t see the electric when writing is score mode or in gallery… I may have deleted the staff, but the instrument still shows up and I want to use it…
Jingle Bell Rock Template.dorico (1.1 MB)

Has the missing instrument been activated for the Layout, for the flow?
I frequently find that a missing instrument (especially one I have added later) has not been automatically activated for a flow where it appears to be missing.

I am not seeing it in the layouts, only as part of the players category…

You have a “-1 staff” signpost at the start of the flow - delete that, and the electric guitar should show up in galley view. It doesn’t appear in page view because both guitars are held by the same player, and by default instrument changes are allowed (meaning only the first instrument held by the player appears in page view, but if you add notes to the 2nd instrument in galley view and they don’t overlap with notes belonging to the first instrument, Dorico will show instrument changes on the staff where appropriate)

Off-topic, but the reason your frames are oversized and extending beyond page margins on your First page template are that their constraints are fixed on all sides, and at some point you’ve changed the page size in the layout. Here’s some information about frame constraints –

Thanks. I see the instrument now; but had not noticed any issues with the framing; I see the overlaps…