The challenge with this issue has been..
From my end I can't recreate the form "hang". From others I know, they also cant recreate this.. but being that our visitors come from all over the world and they are sending us screen shots of a loading screen with a wheel that spins forever, we can tell from our daily sign ups and see there is a HUGE issue going on.
The signup form is from the membership software Restrict Content Pro(RCP). RCP support suggest that it could be a theme or plugin conflict. http://docs.restrictcontentpro.com/article/1587-registration-form-hangs
I have tried the following
1.) I removed all the customizations from the templates as suggested.. waited for 2 hours to see if the sign ups began to happen.. no luck. I have since added small changes back in.
2.) I have turned off as many plugins as I can, but as I am in a live environment and need to stay in one in order to determine if users can sign up.. I cant turn off all the plugins at once without the user experience going really bad. But I am ok with whatever suggestions you can come up with and willing to try anything with some guidance.
3.) One suggestion from RCP support is that themes with page builder might conflict with the form and to switch themes and see if that solves the problem. Cant test this in a live environment as if you switch from Divi to another theme. all the shortcodes code will be displayed, bascially the site would be unusable for anyone.
Users enter info into the sign up form located here
and payment forms
I think thats it in a nut shell.. user sign up forms hang/get stuck and I cant recreate the problem from my end