How come the form won't process for some people?

I made a JotForm to be filled out with payment information and a certain price that had to be paid, if they choose to pay online. Out of the nearly 300 responses to this JotForm, there is one person who will not receive a "Thank You" page, and we will not receive his form or payment. He tried filling out again and the same thing happened. It just make his page look blank, as if there was no form to fill out. Why might this be?

Hello, I cloned your form to check and failed to see any problems. I was able to submit your form regardless if I opt to pay by Mail in check or Pay Online. I saw your Thank You page on both scenarios.

We can better assist you if we know the following:

1. Is your form embedded on a page/website?

   1a. If YES, give us the URL so we can check it directly from there

2. Since this only happens randomly on 1 out of 300 persons as you described, we can both agree that this is a client-sided problem. Do you happen to know what browser that particular respondent was using when he encountered the problem?

   2a. If YES, can you give us the browser version and perhaps the device that visitor used (e.g. if he's on mobile, PC, or any other info that might help)

3. If possible, can you ask the respondent to give you the steps on how we can replicate the problem?

Hoping to hear from you soon.