Drupal 7 entire menu disappeared but showing "array" text

Hi, I have a production drupal 7 website (www.tools4valuechains.org). I have a big issue.
When I visit the website, all main menu disappeared. I see “Array” text instead.
Here is the screenshot which I explained the problem:
Do you have any idea what happened?

Drupal version: 

Source: https://www.drupal.org/taxonomy/term/22/feed