Comments shown, but not the actual text of the comment

We are running Dockerized GitLab CE 8.9.2 Omnibus on-premise.
When we enter a comment for a code line in the commit view, the comment including author’s avatar and text is shown.
When we reload the page (or when somebody else looks at the commit view) the comment is shown with author’s avatar, but the text of the comment is hidden.
Masters can click on “edit” to see (and edit) the comment text, but “developers” cannot do that, hence do not see the comment text.
What can we do?