I use the Divi WordPress theme in many of my sites.
On my personal site, I was using the Divi Contact Form module at the bottom of the home page. It worked great on desktop but someone told me it didn’t work on mobile. Sure enough, they were right! On my iPhone, I got this message after submitting the form:
“Please refresh the page and try again.”
The form didn’t submit, even after refreshing (and even if it had, that would be an unacceptable workaround!)
I couldn’t find the solution online, but after some experimenting, I found a few interesting things. If I disabled my spam blocker, WP Spamshield, the form would work on mobile.
So, I switched to Akisment, but it had the same problem.
Well, I couldn’t have a live site without spam protection, so I checked one other thing: I deactivated WP Fastest Cache, and the form started working again.
So it seems like the combination of anti-spam and caching breaks the Divi Contact Form module on mobile.
This was not a high-volume site, so I just deactivated WP Fastest Cache and left Akisment installed.
If you need a contact form to work with WP Fastest Cache, try the Contact Form 7 plugin. I verified that works on mobile with WP Fastest Cache.
Hope this was helpful! – Brian