Bit of long shot.
When you are editing a book, you're working on a copy of it in a system temporary folder, I have no idea where that might be on a MacOS system, but it looks like you have some sort of permissions issue with it - again no idea why.
But, Calibre has an Environment Variable, CALIBRE_TEMP_DIR, that allows you to set the location where it creates its 'temporary files" see ==>>
Environment variables - there's a link to a 'how to set Env Vars' at the end of that page.
Try creating a directory named say 'CalibreTemp' in your home directory and set CALIBRE_TEMP_DIR to it - now run the editor and do a spell check.
Good luck
BR