Apple Preview is not a reliable PDF viewer, it is better used with image formats. Here is a related topic:
Yes, I know but in Acrobat backgrounds misteriosly disappear
Could you show a screen shot of your PDF in Acrobat or Reader?
If the layer option in InDesign is not set to Print, the layer would not appear in Acrobat (unless the option to export all layers were selected in the export window).
Another possibility is there is a white element knocking out the background, in Acrobat, the page display preference Use Overprint preview should be set to Always.
It looks like your Acrobat overprint preview preference is set to PDF/X only, try changing this to "Sempre" (Always). You may need to close and re-open your PDF after making the change.
I tried. No result : (
Uninstalled and reinstalled, problem solved. Mistery of technology.
Thank you anyway for your help!