What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
What is the form URL in question? If you are using the Single File Upload, you have to make sure that the thank you page is presented and that interruption is not made during the upload process. If you are using the Multi Upload Field, you have to make sure that the progress bar shows 100% else, the file(s) may become corrupted.
One more reason to note that if there's a conflict between your webpage and the form embed scripts so we would suggest using our iFrame Method to avoid that: Getting the Form iFrame Code
Also, make sure that your file upload Max File Size settings is enough. Check this guide: Changing the Upload Size Limit