MasterStudy LMS Fatal error when editing any content

Hello,

The last version of this plugin is 2.4.3, it seems you should update the plugin and please deactivate other plugins before updating it since other plugins may injure MasterStudy. Let us know what editor you are using, sometimes there might be conflicts, as an example MasterStudy is not compatible with Divi builder.

Sincerely

It appears you are also not compatible with Oxygen Builder.

I get the same problem even trying to access certain pages in WP-Admin

possible quick fix

Apparently this is happening because the file /wp-includes/pluggable which contains the function doesn't get loaded until after the plugins are loaded.

Indeed it is. So wrap whichever thing you're doing in a function, and hook it onto the plugins_loaded or init hook. (see the wp-settings.php file)

Example:

add_action('init','do_stuff');
function do_stuff(){
  $current_user = wp_get_current_user();
  // ...
}