well after 45 minutes on the phone with tech support, we discovered that Gmail and other mail services like to insert themselves as default calendar when you enable them as mail.
I have two gmail accounts and a corp account that all come to my ipad and iphone. Each device was set up with a different default calendar and despite m thoughts that I was entering events into the mac calendar I was actually inserting them into the google calendar making them unseen to the mac.
Solution, go into settings:/ mail, contacts. calendars and scroll all the way down till you see default calendar. That needs to be changed to the one you want to match.
Hope this helps someone, it stumped me for a good 4 hours today 😡😛