My Word's spellcheck missing obvious errors. Reinstall? Settings issue?

[varrys]

I'm a writer and editor, and though Word's built-in spellcheck isn't amazing, it's at least been reliable for catching super obvious errors -- until now. I had a document where a comma was inserted into a word instead of at the end, and no matter how many times I run a spellcheck, my machine doesn't find an issue with it. My colleagues run their spellcheck and find it. The word is "is" with a comma in the middle, so "i,s"

 

I have Word 2019. I haven't messed with major settings in Word's Proofing. I started trying to play with a few to get it to find the error, but it won't. I reset the spellcheck and ran it several times on the document. I can't afford to have basic errors like this get through. Do I need to reinstall Word/Office? Or can someone walk me through enabling certain settings to address this?

 

Also while I'm here, if anyone knows of a Custom Dictionary file that is Merriam-Webster's Dictionary, can you point me to that?