Little Black Box with X Showing on Acrobat Pro DC from Illustrator

I'm running Acrobat Pro DC version 2022.001.20112. Whenever I create documents using Illustrator and convert them to PDFs, Acrobat shows these tiny little black boxes with an X in the box. These are throughout the document in random places. I have no idea what could be causing this. Some pages have it, others do not. It shows up on all OS including Linux and Mac. I attached a picture. Can someone please help me with this??