Just a heads up for anyone reading with this same issue. I went back to my excel sheet and sorted the “associate attendee” list so the guests with no “associate attendees” were are the very bottom. This imported all guests except 6 without “associate attendees”. So I just manually imported those 6 that didn’t get imported automatically. No idea why it imported 15 other guests that didn’t have “associate attendees”, maybe a formatting issue in my spreadsheet, but this seemed to be a workaround.
Hope this helps!