Minor formatting issues

Hi

I've converted an AZW to ePub (first time using Calibre) but have two minor formatting issues.

Firstly, some pages have a thicker margin at the bottom of the page, not necessarily where there is a paragraph break. Also, randomly page numbers are appearing on screen, about a third of the way down the right hand side, being imposed over text. This is on a Kobo Aura.

Thanks in advance
Neil