Illustrator file only previews in Separation Preview mode.
I have an Illustrator CC 2018 file saved as .ai with PDF compatibility. It is just a rectangle with a pattern fill. The pattern uses simple shapes and a compound path filled with process black (which overprints) and a Pantone solid. When I place the file in InDesign CC 2018 the cursor previews the file, but only a blank image shows. InDesign will only preview the file when Separation Preview is on.
Odder still, whatever the image is behind does not show. So if I send the image to the back, everything is hidden. If I bring it to the front everything is visible, except the image. With Separation Preview on everything looks as it should.
I saved as IDML and deleted preferences. The problem is still occurring. This also happens when placing the Illustrator file in a new document. The file behaves normally when I expand the pattern.
Cross posting in Illustrator.

