Improper "transparency knockout group" support: transparent objects where opaque ones expected
PDF with opaque objects are rendered transparent with poppler. Adobe Acrobar, FoxIT and Sumatra PDF renders the opaque objects properly.
Correct Sumatra PDF rendering:
Search for “transparency knockout” on both (https://therion.speleo.sk/wiki/contrib:externalviewers) and (https://helpx.adobe.com/illustrator/using/transparency-blending-modes.html)