Originally Posted by PetMice

You could make sure that you haven't got changes in line spacings somewhere in the pages shown. Also, if you have some inserted scaleable object (image, table, equation?) near the top of the right hand page (not visible in your image) this could push the text below it down by an amount that does not equal the set line spacing, causing it to lose its alignment with the left hand page, in which case you might restore the alignment by adjustments to the inserted object.
(Should it not be "There is a wide variety of researches..."?)