Has your EPUB been created with a page-map.xml file ?
https://wiki.mobileread.com/wiki/Adobe_Digital_Editions have a look at Epub Extensions, Page Map.
If so this could explain what is happening. If so you could delete the file using Sigil so ADE would display the "correct" page (bear in mind that in any case for an EPUB displayed by ADE a "page" is 1024 characters, irrespective of the text size etc)
BobC