I dont have v 20 anymore on this machine, so tested in v 2015 and it work like a charm, no problem
What i do remember was more common earlier is that after a Print to PDF, some object could "hide" and sometimes absolutly everything in P Space.
So i used Ctrl + a and then Bring to Front, so maybe something like that could be related to your problem.
V18, V19, V20, V21, 2015/ 16/ 17/ 18 Pro. Platinum
Deluxe V20, V21, 2015/ 16/ 17
Windows 10 Home Premium 64 bit, 32 GB
NVIDIA Geforce GTX 780m, 1 GB