"read more" not coming up for article

My articles added to the front page are all showed in full content without the “read more” link.
The settings are as follow :
/admin/structure/types/manage/article/display : body = default
/admin/structure/types/manage/article/display/teaser : body = summary or trimmed
How to activate the “read more” link?

Drupal version: 


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