Fusion Builder or Theme Options Not Working With WordPress 4.9
Issue 1 - WordPress Install Was Updated To 4.9+ But Avada Is Not Updated To Latest Version 5.3.1
SOLUTION: Update to the latest version of Avada v5.3.1 which is 100% compatible with WordPress 4.9+. Update Avada along with Fusion Builder & Fusion Core plugins and make sure to clear all forms of cache (browser, plugins, server). Then go to Avada > Fusion Patcher and apply any available patches. Patches are applied at the click of a button as explained in this help file -> http://bit.ly/1NAWVwM
When updating your theme always ensure that follow the correct instructions and are aware of the below information:
Issue 2 - WordPress Install Was Updated To 4.9+ & Avada Updated to 5.3.1 But Issues Remain
SOLUTION: This is a confirmed WordPress core bug involving language files: https://core.trac.wordpress.org/ticket/42574. "MediaElement upgrade causing JS errors when certain languages are in use e.g de_DE-formal".
The issue applies to any language file in this format: de_DE-formal. To resolve this, change the WordPress Core to the regular format: de_DE by changing the language in the WordPress admin area (Settings > General). For example, if currently set to "Deutsch (Sie)" instead select "Deutsch".