Total referrals is way too low

I’m looking at the Sites Stats page of Fear of Landing for Sunday the 21st of Feb 2016. This day highlights the problem but it seems clear that the problem is always there.

The Total views referred by links to your blog for that day is 375 whilst the Total views of posts on your blog is 2,520. A view of his page can be seen in this screenshot.

The issue is highlighted by the fact that the post with the highest hits was an old post, linked to from imgur.com. Other than that site, there seems to be no reason why that particular post would have been highlighted that day. I would have expected the referrals from imgur.com roughly to have equalled the hits to that post but there is a big discrepancy.

For reference, the site is running as part of an MU install under Nginx and php-fpm.

What am I missing? And where did the other 2,000+ hits come from?

Cliff.