1px and 2px lines show incorrect thickness when converting a high resolution pdf into a lower resolution pdf.

Hi all,

Converting a higher resolution pdf into a lower resolution pdf file is causing 2px lines to appear in random different thicknesses. Sometimes they even disappear. I also have 1px strokes framing some photos and some of those lines disappear too. I have already changed the preferences of Acrobat Pro DC to uncheck "enhance thin lines" and "smooth line art" and has not made any difference.

Anyone out there know how to sort out this issue?

Many thanks