Note (in the ePub) the class names of the html elements preceding and following the gaps:
<p class="
blah-blah">
Open the css stylesheet and locate the class names from above.
In the properties for those classes, look for "margin", or "margin-top", or "margin-bottom" attributes that are
not zero (0).
Make them zero, or reduce them or remove those attributes until the spacing looks how you want it to.