While inspecting tuleap.net error log I found this:
2017/10/18 13:07:57 [error] 22943#0: *226784 FastCGI sent in stderr: "PHP message: PHP Notice: Undefined index: forum_id in /usr/share/tuleap/src/common/include/URL.class.php on line 119" while reading response header from upstream, client: , server: tuleap.net, request: "GET /forum/message.php?msg_id=2583
It happens when you are accessing a message of a "news forum" :poo: directly