7 votesMarc Cuong commented
In InDesign 2018 (v.13), I had similar problem with pixelated images (which links were updated) appeared suddenly in my exported PDFs (print), no matter how high quality preset I used . To fix it, I had to trash InDesign current preferences and cache manually to get a fresh start. In Windows, I closed InDesign, I renamed the 2 directories (e.g. suffix with .bak):
then start InDesign again to find it fixed. The tutorial to do that in MacOS can be found on Internet as well.
Otherwise, the workaround is to export to "PDF (interactive)".