I entered chords in another part that I have since deleted. (The chord symbols appeared in other parts automatically.)
I’m unable to enter chords now. Green boxes with chord names appear, and nothing changes when I enter chords.
Chords do not appear in printed copies.
The green boxes represent chord symbols that are hidden for that instrument. Go to Setup mode, right-click on the relevant player in the left panel and you should see a context menu. In the Chord Symbols section of that context menu ensure that the correct options are set, e.g. if that’s a non rhythm-section instrument you’ll need “show in all instruments” selected.