hap
as BR said, we dont have any ideas based on what you supplied.
I am HTML (and CSS, since I came to here to MR) literate, so I look at the EPUB code. there may be a stray pagebreak_befor: always (but for the life of me, can't see why that would not mess up the EPUB display also.
Validate your EPUB and CSS. Various render engins (and conversion engines) will ignore styles that have errors in syntax or (crazy) values (Validate won't find the insane values)