Hi,
I tested this in Chrome, Win 10 and diagrams.net 15.5.5 and couldn't reproduce the issue.
I see you are using draw.io version [15.4.1].
Could you update to the latest and test again? (just do hard reload and you should be able to see 15.5.5 under Help menu)
Also, clear cache and temporarily disable browser extensions if you have any (if updating doesn't help)
If nothing helps, try with File > Export as > Advanced > PDF and File > Print > Print (change paper size) > Print to PDF/Save as PDF.
Regards