My math teachers like to have the students take pictures of their work and submit the file using the App with their phones. We have run into this issue with multiple students. They take the picture and turn it in via the app and it says turned in (teachers have visually watched student turn it in). On the teacher side they never see it and it shows as missing. I have asked the teachers to restrict the file type to JPG (just in case it was an issue with the Apple phone picture file type) and that did not help.
How are students submitting the file? Is it an assignment or upload through a quiz? Is this just happening on iOS or Android too?
Have the students had any success using the scanner tool on iOS? This might be more reliable than an image file.
I would suggest trying this out as well.