Hi letterwoman ,
would the pattern show if you export the page with the placed AI file as e.g. PDF/X-4 ?
Hm. I could be on the wrong track, but I remember a case where the preview of a placed AI graphic was only partly possible if an Illustrator pattern had some elements that were set to overprint. This bug should be fixed with InDesign CC 2018.1. Perhaps it came back in a different form with InDesign CC 2019 and Illustrator CC 2019?
Details on the bug and a workaround for the issue here:
Zoom Factor issue: Linked Graphics from Illustrator vanishes in Indesign. Win7/CC2017
Possible workaround: Add transparency and switch to Overprint Preview.
What will happen if you add a small rectangle to the spread where you placed the AI file, filled with [Paper] and blending of the Effects panel set to 0% ? Would the pattern show up if you enable Overprint Preview?
Could you open the AI file, isolate a detail where the issue is showing, copy and save that to an extra AI file that you can make available for testing on Dropbox or a similar service and post the link?
FWIW: Just tested the linked AI file from this old thread on my old InDesign versions on Windows 10.
Cannot see an issue. But I definitely saw and documented the issue back then on Mac OS X with e.g. InDesign CC 2015.4. Also with InDesign CC 2017.
Regards,
Uwe