Help! Gray Background Appears When Clipping Transparent Images in Illustrator

When I clip a transparent image in Illustrator and export it (usually as a PDF), everything looks fine in Adobe Acrobat. But when I open the same file in Outlook, Microsoft Edge, or other web-based viewers, I see a gray background behind the clipped image. I understand that Acrobat has superior rendering capabilities, but clients often view PDFs in their default apps, so I need the file to look correct everywhere, not just in Acrobat.

NOTE: It only happens with some of the images and not others.

1. I remove the background from an image in Photoshop.
2. I save it to my Creative Cloud Library.
3. I place it into Illustrator from the CC Library.
4. I apply a clipping mask to crop it.
5. I export the file as a PDF or PNG.

The only reliable fix I’ve found is to drop in a PNG of the transparent image directly into Illustrator instead of using the CC Library asset. This seems to preserve transparency better across all viewers. This is not efficent for my workflow however and I need a fix that works with the cc lib. Help!