I've got a number of online maps with features that contain attachments to PDF and jpeg files. Some of these links are not loading properly. I either get a warning that "the image ____ cannot be displayed because it contains errors" or a page loads with Wingdings type symbology (picture below). It seems to correspond to the browser being used: iOS Safari seems to load all attachments without problem, Chrome handles most attachments, Firefox handles fewer than Chrome, and nothing loads in IE/Edge.
Is there something I can do aside from installing Safari on all my users computers?