Modifying margins, I got this. Left and right margin values are swapped. Here, left input box controls right margin and vice versa, as you can see on the image. E.g. left margin should be 14mm, but instead, right margin is 14pt.
I cannot say exactly how this happens but I think I get this sometimes when starting a document as facing pages document and changing to single pages afterwards.
Sometimes I would switch from 'facing pages' document to single pages document and still see 'inside' and 'outside' margin input boxes.