This feels vaguely wrong:
Slashes are displaying as treble clefs. Yes, I restarted the computer after updating to 2.2.10.
Have you made any edits to any of the noteheads in Engrave > Notehead Sets? If so, you might want to try resetting them back to the factory default in that project.
I’ve not changed any noteheads, no.
It was an XML import, but it displayed fine before the update.
Do slash regions look OK in other projects?
They don’t, actually! Even from a new project. 
So it’s definitely a font problem, then. Can you please look in your Windows Fonts folder and see what versions of Bravura and Bravura Text you have installed? It should be version 1.276 for Bravura and version 1.277 for Bravura Text.
Bravura version is 1.204 (Bravura Text is 1.277). Not sure why; I’ve always updated and restarted as instructed.
Do I need to run the update again?
Try just installing the latest version of the font manually in the Windows Fonts folder.
Bravura.otf.zip (330 KB)
That fixed it, thanks!
Not sure how the font failed to keep current, but I’m happy to let sleeping dogs lie…