I’ve noticed this behavior sporadically before and ignored it, but I just clicked over to Scrivener and something like a dozen words across the document are underlined in red and being marked as incorrect. For some reason the spellchecker is only spellchecking the first half of these word. So for the word ‘deliver’, the spellchecker is looking for ‘deliv’ and of course not finding it. I’ve included a couple images to demonstrate. Definitely a bug somewhere along the line, either in Scrivener or MacOS.