Sometimes while trying to activate Mega Menu checkbox unchecked after menu save.
If you enable debug, you will see the following error:
PHP Warning: Unknown: Input variables exceeded 1000.
You can fix this in 2 ways:
- Remove unused menu items
- If you need to have all menu items, you need to increase PHP value max_input_vars. By default on the most of hostings used 1000 value, you can try to increase it to 3000.
Add the directive into php.ini or place following lines into .htaccess:
php_value max_input_vars 3000
php_value suhosin.get.max_vars 3000
php_value suhosin.post.max_vars 3000
php_value suhosin.request.max_vars 3000