The issue is that creation of artifact with lightwindow doesn't have format for text fields. When the payload is sent, it's not complete (format is missing) and this raise a Notice.
2021/03/22 15:25:13 [error] 12034#0: *85 FastCGI sent in stderr: "PHP message: PHP Notice: Undefined index: format in /usr/share/tuleap/plugins/tracker/include/Tracker/FormElement/Tracker_FormElement_Field_Text.php on line 604
PHP message: PHP Stack trace:
PHP message: PHP 1. {main}() /usr/share/tuleap/src/www/index.php:0
PHP message: PHP 2. Tuleap\Request\FrontRouter->route() /usr/share/tuleap/src/www/index.php:49
PHP message: PHP 3. Tuleap\Request\FrontRouter->routeHandler() /usr/share/tuleap/src/common/Request/FrontRouter.php:108
PHP message: PHP 4. Tuleap\Tracker\TrackerPluginDefaultController->process() /usr/share/tuleap/src/common/Request/FrontRouter.php:248
PHP message: PHP 5. TrackerManager->process() /usr/share/tuleap/plugins/tracker/include/TrackerPluginDefaultController.php:45
PHP message: PHP 6. TrackerManager->processSubElement() /usr/share/tuleap/plugins/tracker/include/Tracker/TrackerManager.class.php:163
PHP message: PHP 7. Tracker->process() /usr/share/tuleap/plugins/tracker/include/Tracker/TrackerManager.class.php:145
PHP message: PHP 8. Tracker_Action_CreateArtifact->process() /usr/share/tuleap/plugins/tracker/include/Tracker/Tracker.class.php:782
PHP message: PHP 9. Tracker_Action_CreateArtifact->processCreate() /usr/share/tuleap/plugins/tracker/include/Tracker/Action/CreateArtifact.class.php:43
PHP message: PHP 10. Tracker_Action_CreateArtifact->createArtifact() /usr/share/tuleap/plugins/tracker/include/Tracker/Action/CreateArtifact.class.php:53
PHP message: PHP 11. Tracker_ArtifactFactory->createArtifact() /usr/share/tuleap/plugins/tracker/include/Tracker/Action/CreateArtifact.class.php:84
PHP message: PHP 12. Tuleap\Tracker\Artifact\Creation\TrackerArtifactCreator->create() /usr/share/tuleap/plugins/tracker/include/Tracker/Artifact/Tracker_ArtifactFactory.class.php:366
PHP message: PHP 13. Tuleap\Tracker\Artifact\Creation\TrackerArtifactCreator->createFirstChangesetNoValidation() /usr/share/tuleap/plugins/tracker/include/Tracker/Artifact/Creation/TrackerArtifactCreator.class.php:2