I've been creating buttons on my pages that early readers can use to click right to an assignment or discussion. While they show up on a number of the ipads, some show a box with a "?" inside. In addition, I have made buttons that show up in my course (on an ipad). I shared them to commons. But when used by the next teacher they show up as "?". Is there a way to correct this? Is there a certain file size to stay under for jpegs or buttons? Is there a certain version of the iOS on iPads that this is a problem?