Issue has been introduced by git #tuleap/stable/27e0eaaf8902e142c30c6a49daadb1c4dedbe811
FastCGI sent in stderr: "PHP message: PHP Fatal error: Uncaught TypeError: Return value of Tracker_FormElement_Container_Fieldset::getLabel() must be of the type string, null returned in /usr/share/tuleap/plugins/tracker/include/Tracker/FormElement/Tracker_FormElement_Container_Fieldset.class.php:220#012Stack trace:#012#0 /usr/share/tuleap/plugins/tracker/include/Tracker/FormElement/View/Admin.class.php(88): Tracker_FormElement_Container_Fieldset->getLabel()#012#1 /usr/share/tuleap/plugins/tracker/include/Tracker/FormElement/View/Admin/CreateVisitor.class.php(33): Tracker_FormElement_View_Admin->fetchLabelForUpdate()#012#2 /usr/share/tuleap/plugins/tracker/include/Tracker/FormElement/View/Admin/CreateVisitor.class.php(69): Tracker_FormElement_View_Admin_CreateVisitor->fetchForm()#012#3 /usr/share/tuleap/plugins/tracker/include/Tracker/FormElement/Tracker_FormElementFactory.class.php(1586): Tracker_FormElement_View_Admin_CreateVisitor->display(Object(TrackerManager), Object(HTTPRequest))#012#4 /usr/share/tuleap/plugins/tracker/include/Trac" while reading response header from upstream, client: 2a01:e35:2e50:e330:dee2:9d3b:ce06:f546, server: my.enalean.com, request: "POST /plugins/tracker/?tracker=666&func=admin-formElements HTTP/2.0",
Reference: https://logs.enalean.com/messages/graylog_12/67463ef0-99a2-11ea-832d-0242ac140012