ePub line spacing problems, but no problems in .mobi

I am having some issues with my ePub compile that I am hoping someone can help with.

I’ve already compiled one book into .mobi and .epub with no problems and regularly compile for editing and proofreading purposes, but this time it is not going quite as smoothly.

This time, the Kindle book looks great, no problems at all. It’s already uploaded, viewed on my Kindle, viewed in Kindle Previewer, everything’s good.

However, the epub - while it passes epubcheck - looks awful in the Nook previewer, the lines are all on top of each other (see screenshot). This is an improvement from the first epub, which was all centered in the Nook previewer AND on top of each other.
Screen Shot 2014-01-13 at 10.41.11 PM.png

When I email it to myself and open it in iBooks, there is a similar spacing problem, although not nearly as drastic. (See second screenshot.)

Any ideas as to what I could have done wrong, or what I can do differently in the epub compile to resolve this issue? Thank you in advance for any ideas or suggestions.

I would still love an answer to this. I could never resolve it and ended up having to pay someone to generate the epub. This is annoying because I have touted Scrivener’s ability to export to epub as a reason to work in it and already successfully did this for one book.