Lattira Spec and NBS Chorus are no longer compatible with Autodesk Revit 2019. It is not compatible even with previous versions of the NBS Plug-in for Autodesk Revit.
Lattira Spec and NBS Chorus are supported in newer versions of Autodesk Revit. Please see the National BIM Library for the latest information about which versions.
Background
Lattira Spec and NBS Chorus use a web framework called 'Angular'. Supported versions of Angular do not work with older browsers, such as Internet Explorer 11 and the browser version provided with Revit 2019.
Chorus in Revit 2019
Chorus will not load in Revit 2019. It will appear as a blank white panel.
Screenshot showing the specification panel in Autodesk Revit 2019.