Your form may have expanded past the point your current server configuration allows.

1. Go to edit your long form. Click on "Settings" and select "Load and save form builder page with Ajax".
2. If the problem persists, you will need to increase the post_max_size in your php.ini to 32M or 64M. If you're not sure where to find this file, please contact your webhost for help.
3. Some versions of PHP also have a max_input_vars setting. If you have this option in your php.ini, increase it to at least 2000. The option max_input_vars is only present in the php.ini file in php 5.3.9 and up. Any version before that the max_input_vars is not in the php.ini by default. In versions before 5.3.9 you have to manually add max_input_vars=2000 (or 3000 or higher) in the php.ini file and restart the apache service. This should resolve the issue of fields not saving properly on a long form.
4. Some servers use Suhosin. It includes its own set of limits. If your server uses it, try turning it off.
5. If you have changed these settings and the fields still aren't saving, your server settings may not being used in your WordPress admin area. On some hosts, you may need to create a php.ini file with these settings and place it in your wp-admin folder.
6. Browser extensions and add-ons can dramatically affect page loading and responsiveness. Try disabling all browser add-ons and extensions or using a different browser.