Request easy way of unhiding a staff set to "Hide when empty"

It appears you set that staff to always hide when empty in its Staff Properties. It's empty, so it got hidden. So, not a bug.

Getting the staff back is currently a little tricky. The way I know is to enter a note on it by going into note input mode on the staff above, then hitting Alt+Down to move the cursor to the missing staff, then entering a note. Then it will appear, and you can access its Staff Properties.

Ultimately, it might make the msot sense to implement the controls requested in #74181: Up/down next/previous staff navigation buttons in Staff Properties dialog, similar to existing feature in Measure Properties. I'll leave this feature request separate, though, as there might well be a more direct solution (like a checkbox in Style / General to force all staves to be displayed).