I replied more fully in a separate email about the sample. In your document it was not a matter of even- or odd-numbered pages. Sometimes one dropped a little lower; sometimes the other.
It is the interplay between line spacing and paragraph spacing. The paragraph spacing is not (nor should it be) an integer multiple of the line spacing. This means that on some pages where you have more paragraph breaks than on others, the text goes a bit lower at the bottom of the page or the next line won't quite fit. In many instances, where there would be room for a full line under the text that is there but it still breaks, that is the "widow and orphan" formatting.
If you made your space between paragraphs an exact multiple of the space between lines chances are that you would not observe this, but your text would look choppy, like text generated on a typewriter.
You also could try vertical justification, but I wouldn't recommend that.
Alignment / Justification of Text in Microsoft Word. If you do, remember that it is a section property and try it in a COPY of your document.
Attached are three screen shots from your document. The first and third show the odd-numbered page lower, the second shows the even-numbered page lower. The third one is definitely the result of widow and orphan setting.