Why uploaded files are not accessible?

I created a form that let my student upload homework (zip file)

https://form.jotform.me/80513770484458

Last 2 week, some files are missing

This is the message when i tried to download

404 Not Found : /jufs/gindrako/80513770484458/3950351167813849111/c5-out.7z

I'm afraid that, when files failed to upload or there is any network issue during upload, we are not able to retrieve them. The only way is to ask your users to re-upload the files.

If you have any further questions, please let us know.

Thank you!