This has probably already been solved, but since it is an open question I will try to answer it anyway.

I think this might be caused either because the files are not added to the assets. But after checking the github, this can be ignored, since the xml clearly adds the js and css to the assets.

Another problem might be that you copied the files over as root, but run Odoo as another user and the user might not have access to the folder.

Yet another reason could be that the module was moved, and it is no longer in your addons-path, therefor the files could not be found.

Now, as I mentioned earlier I checked the github and noticed that there have been a few adjustments since this question was asked, so it might also be possible that it was just a faulty module back when this question was asked.