It sounds like the effect of the long paragraph bug in the epub reader, but might also be the widows/orphans settings in the book.
Kobo devices have seperate readers for Adobe epub (epub) and Kobo epub (kepub) format books. The long paragraph bug affects epub books which have paragraphs longer than one full screen of text. It doesn't affect the kepub reader. One approach to avoid this problem is to sideload your books from Calibre in kepub format using the Kobo Touch Extended driver. The other approach is to apply the page break patch for your firmware version, which often (but not always) fixes the problem for epub format books.
To find out about using the Kobo Touch Extended driver to sideload kepub format books see:
https://www.mobileread.com/forums/sho...d.php?t=211135
For instructions to apply patches to firmware version 3.2.0 see:
https://www.mobileread.com/forums/sho...d.php?t=234764
The widows/orphans settings for the book can cause a paragraph to be pushed forward to the next page to avoid a single line being displayed at the bottom ot top of the page. The most noticable effect of this is the extra few blank lines at the bottom of a page. You can turn this feature off by adding the line
p,div {orphans:0;widows:0;} to the Extra CSS field in the Calibre Look and Feel conversion settings before converting the book.