Just to note that I think I might have had a similar problem yesterday. Someone suggested it might be caching, which I let convince me, but I had communication via Facebook, etc, of multiple people reading a post, and WP stats weren't showing as many hits as I knew there had been. And my hit count on that post was pretty low by comparison to comparable posts. And I had a relatively high number of overall hits on other posts that day, but zero referrals from Facebook, which never happens one a day I post a new post.
I suspected, and still do, that Facebook referred hits weren't being counted for at least part of the day yesterday.