Publish to PDF issues, - CorelDraw 2019

i am designing billboards regularly and always publish to PDF using the same settings, now suddenly, with one specific design the PDF comes out blank.

a similar design comes out perfectly, I've tested over and over again, even redesigned the one with the problem from scratch, but still the PDF comes out blank, but when publishing previous designs to PDF result is fine.

can someone please help with explanation of what I am doing wrong?