Can't make a fixed layout epub.

I'm using the latest version of InDesign, I'm trying to make a fixed layout EPUB of a book for a client.  It goes through the process like normal, but the first few pages are too big for the ebook window, and the fonts are all different weights. I made a fixed layout EPUB of the same book in May, and it was perfect. I have now tried the second book in the series, and again, the same result: the first few pages are too big, and the fonts are messed up. I have now tried a totally different book from a different publisher, and it's the same; the first page is too big, and the fonts (different from the other book) are also screwed. 

It's getting really frustrating, everything I change in the settings, and it produces the same epub. Can anyone help?