This sounds like the same thing that is happening to me. Between 1/4 and 3/4 of the page show up a second later than the left of the page. On paging back, it's the left side that lags behind. It's very distracting.
This began with ios8. I've been hoping for a fix, but I'm starting to loose faith. My impression is that it's a bug that only appear for some of us, and the developer seem to be busy with his new app.
According to
this post, restarting the app helps until they open a new book, but this doesn't change anything for me.