It’s probably easier to say if you share your file. If it’s not too heavy, just by dragging it here, or using wetransfert or similar solution.
You can even remove the extra pages and leave just the culprit.
You’re right, it shouldn’t change dimension. The only thing I’m thinking of right now is that you have exploded the drawing and changed the unit of the result… and still, it should retain 20"
oh wow! What an easy fix. I never ran into this problem, when working on a file on my own, I got this from my assistant and was totally thrown off by it. Thank you.