Do you have multiple PDF creation software/apps installed on your computer? Like free ones?
In the past i found some of the free or basic PDF software apps can cause problems with PDF exports (not just exported from SketchUp or Layout, but from many programs).
My solution is to uninstall or reinstall your PDF software…Try to have just one PDF creation app (ideally one of the good ones ike Adobe Acrobat or Bluebeam Revu) if possible. And make sure that you keep them updated once you have installed them.
Once you have done that, if it still does not work then try to re-install LayOut then try again.