I had a similar problem trying to animate a book flipping pages. At the half way point I had to update the text to show the backside and update the back pages.

I had a similar problem trying to animate a book flipping pages. At the half way point I had to update the text to show the backside and update the back pages. However no matter what I did, I could not get the update to sync correctly with the page being exactly half way. There's probably a solution but I just gave up