I have exactly the same problem as @jackyspeed, using Opera 54.0. However I had this issue since it was introduced.
Have tried it on several computers and the problem persist. Environment is:
Windows 10 (several versions)
Opera (several versions)
Adobe Acrobat Reader (several versions)
Print to PDF always works, with the limitation of not retaining page layout.
Save to PDF works for short web pages only and fails to save the entire page on long pages (please try pages that at least 24 pages long.