Spell Check in Scrivener 3 not picking up any typos?

I went to go spell check my manuscript using the spell check function (Edit → Spelling & Grammar → Check Document Now), and it will highlight perfectly normal words like “to” (which makes NO sense) and some of my character names (which makes sense since I write fantasy). But the function will only highlight ONE “error” per chapter document in my manuscript. To test the spell check function one last time, I actually inserted a typo (“adn” instead of “and”), and the spell check didn’t pick it up.

Am I missing something? Or is there a bug?

Spell checking is provided by the system software, not by Scrivener. Problems with it have been noted. See here: https://scrivener.tenderapp.com/help/kb/macos-troubleshooting/known-issues-2