We're hosting 15mb of video files on that landing page. Netlify says we've had 2.2 TB of transfer out but dividing those numbers gives many more uniques than we've seen in the landing page analytics :/
If anyone's interested, it is likely that the missing traffic is coming from people with blocker scripts that prevent analytics. I've moved the media files from the landing page over to a S3 bucket behind Cloudflare as suggested.