Can't edit velocity on just one of my MIDI tracks

I’m not sure what’s happening, but Dorico won’t let me edit, draw with the pencil, the velocity for my cello track. I can edit with the pencil the velocity for my other tracks.

When I draw it starts showing the vertical lines, but as soon as I let go of the mouse button, they disappear.

What should I check that would be preventing me from editing it?

The simplest way to help us diagnose it would be to attach the project itself here, or a cut-down version of it that’s sufficient to allow us to reproduce the problem.

I think I may have figured out what was going on. I’m using key switch samples from EastWest and until I assigned an expression (ex: detached) to the notes in question I could not draw velocity.