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.
I've checked your JotForm submissions and it seems that they are submitted at different times.
I've tried submitting your form and I was not able to replicate the issue with the form. Generally, this issue happens when the user pressed back button on the browser after submitting the form. Did you make any changes to your JotForm recently including to change Thank you page?