This is difficult to help with without accessing your site. When something that's been working all along suddenly stops working, it's usually due to a conflict somewhere, whether that be server or plugin level. Unless you've changed your code recently, reviewing the code isn't much help to solving the problem. I suggest you enable WordPress debug and step through the standard WordPress self-troubleshooting steps.

1. When did you first notice the problem?
2. What changed in your system before the problem started?
3. Do you have system backups from before the problem started?
4. Is your site running on the latest versions of PHP, WordPress, and Formidable?
5. Are there any fatal errors recorded in the server error logs or WordPress debug log?
6. Are there any jQuery/JavaScript errors in the browser console?
7. Have you switched to a WordPress default theme to test for theme conflicts?
8. Have you tested for plugin conflicts by deactivating all of them and re-enabling them one at a time?

All of this troubleshooting needs to be done by you or someone you hire that can access your server to help find the problem. As community volunteers, this is much more than we can help you with without a paid project. You could try opening a support ticket with Formidable, but since your issue is about custom code, they may not be able to help and will only redirect you back here to the volunteer community. If you need developer assistance, please visit the Formidable Masterminds Developers Directory to search for resources.