I have a course where two students submitted files that I cannot view in the grader - when I open the grader, it will just be stuck at "generating PDF" forever.
The really weird thing is that the files themselves do not seem to be the source of this problem - when I submit the identical files with a test user in the same assignment, the grader opens them just fine.
Also, when I submit a different file in the same attempt for a student where it does not work, it will not work either.
The only way to get the grader to display a submission is to allow that student another attempt and then re-upload the file - then even re-uploading the same file will work just fine.
I think that the initial generation of the PDF from the submission might have failed, or that some existing annotations on the file might be broken. Is there any way to delete corrupt PDFs that were generated for a submission or by annotating?