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 did check your form in my iPhone device and it seems to work as expected. While I sign in the widget, it does not move the screen.
Please be noted that the height of your "Smooth Signature" widget is too small. That could be the reason why the screen moves. I would suggest you to please increase the height of the widget and that should most likely solve your problem. I would also suggest you to make your form mobile responsive as well. Please check the screenshot below:
Please take a look at the following cloned form and see if this works as expected: http://form.jotformpro.com/form/52082264835961?
Feel free to clone this form for a closer look. The following guide should help you in form cloning: http://www.jotform.com/help/42-How-to-Clone-an-Existing-Form-from-a-URL
Hope this helps.
Do get back to us if you have any questions.