[Resuelto] I found the ‘wp-config.php’ file, but there is no ‘define(‘WP_DEBUG’, false);’.

Background of the issue:
I found the ‘wp-config.php’ file, but there is no ‘define(‘WP_DEBUG’, false);’. I am working on a site under development. When I click WPML on the dashboard of my website, it jumps to a page which shows '504 -Gateway Timeout'. When I click posts, pages, appearance on the dashboard, everything goes right.

Symptoms:
Clicking WPML results in a 504 Gateway Timeout error.

Questions:
Why does clicking WPML result in a 504 Gateway Timeout error?
How can I resolve the 504 Gateway Timeout error when accessing WPML?