When using Scene Viewer in ArcGIS Online, the Designer toolbar is not initialized nor accessible when the Welcome Screen does not show correctly.

Solución alternativa

Click on New Global Scene or New Local Scene in the New Scene menu next to the user's menu.

This fixes the issue as the presence of ?viewingmode URL paramater seems to bypass the bug, e.g. https://rqa01bi-rqa01bi.apps.openshift48release.esri.com/gis/home/webscene/viewer.html?viewingmode=global

Pasos para reproducir