Registration Page Not Working

This registration page was working, however, in the last 24 hours, it has stopped.

When you try to register as a new user, you fill in all the fields, hit the register button and then it just reloads the form. I have tried it on multi emails addresses and browsers. I have also tried deactivating wordfence and really simple SSL

It should redirect to the login page: https://ostrero.com/log-in/

Any ideas why this might be happening?

The page I need help with: [log in to see the link]