according to the SU 2017 Release Notes:
Standardized Product Content Locations
We have standardized where product content, stuff like collections of
components, materials and styles are stored on the file system.
On Windows, we moved the default content that comes with SketchUp
(Components, Materials and Styles) out of the Program Files directory
and placed them in the ProgramData directory. And on both Windows and
Mac, we created Components, Materials, Styles and Templates folders for
your user related content. By default, these folders are in the
Windows: C:\Users\\AppData\Roaming\SketchUp\SketchUp 2017
Note that if you store your content in these folders, it will show up in the
Components, Materials and Styles browsers without you having to do
anything and your templates will show up on the Templates pane as well.
Storing content in the %APPDATA% path mentioned above doesn’t trigger anything in the content tabs of SU. Storing to the %PROGRAMDATA% path still works.
This seems to be either a bug or a wrong documentation of the path (2 slashes wrong anyhow).