I have 2 gravity forms on my website - a contact us form and a paypal form.
Both work fine on my PC, but when I go to my site on a Samsung Galaxy tablet, both forms often reject the user's email. (Often but not always!).
As a test, I made the email not required. Then, if I leave the email blank, the form is accepted. But if I enter any email address, it tells me that the email is invalid, even although I marked it as not required.
I am using the latest Wordpress and the Headway theme.