Sometimes our wordpress menu drag and drop functionality stops working suddenly. Most of the times it is the result of Javascript concatenation used for admin area.

As per this JavaScript files are concatenated to one URL to make admin faster. In some of the cases menu drop down stops working due to this concatenation. So to resolve this we can disable this feature using the below mentioned code in our config.php file : 

define( 'CONCATENATE_SCRIPTS', false );

Note : Put the above mentioned code just below this line :

define('DB_HOST', 'localhost');

This will stop that concatenation of JavaScript and the issue got resolve.