Save and continue not working for a user

I have a user who is on a mac, filling out a long form. She has tried to submit three times, and the form fails because of an issue with a file upload. Every time that she goes back in to the form, all of her answers have disappeared, and she has to fill out the whole form all over again.

I asked her if she is doing private browsing or incognito, and she says no.

What might cause this feature not to work? I purposely did this for my users to save them this type of aggravation.

Thank you so much.

Since the data is saved in the browser, if the users browser cache/cookies are cleared or do not allow for saving, it would prevent the save and continue feature from working.  Private or incognito mode, as you mentioned, would prevent this as well. 

If you want a permanent save and continue, you can allow users to submit partial forms and return to them later via an edit submission link:

https://www.jotform.com/help/40-How-to-Let-Users-Update-Their-Form-Submissions-at-a-Later-Date