Great speed test – but loads extremely slow for user

Hi,
Giving Nitropack a go. Switched from W3 Total Cache.
Page speed is incredible at 100%. But when going to a browser as a user it takes ages to get past the page loader.
Strangely, if you start scrolling down the page it loads immediately.
Any advice?
Thank you.

The page I need help with: [log in to see the link]