macOS Catalina: Preview > Print... > Save As PDF, not really working
I have experienced a problem similar to yours. 

Unfortunately for us, there seems to be no solution, but "the answer" to our questions was revealed in my telephone call to Apple Care. During this support call, a "second-level" tech support person stated:


  "Apple doesn't actually support PDF files with Preview. There is nothing we can do to help you."


UPDATE/EDIT:

A subsequent call to AppleCare got me to a different support person who was not afflicted with an attitude. Apple subsequently reviewed a copy of my PDF document, duplicated the behavior I saw, and collected some "system data" from my Macbook. I finally got the results of this, and Apple has indicated they have found an issue that will be addressed in a future update.