The number of scans that you see on the Analytics page shows the count of how many times users have scanned your QR Code and viewed the landing page. Note that everytime the landing page is loaded, irrespective of whether the same user scanned the QR Code again or the user simply refreshed the page, it will be counted as a scan.
On the other hand, RSVPs are sent only if the user has selected a response (accept/decline) and clicked on Submit button.
So, it might be possible that the users scanned your QR Code, viewed the landing page but didn't choose to submit a response. In such cases, you'll notice that the number of RSVPs is less than the number of scan.