In this folder you can find the libraries LPub3D uses:
C:\Users\[your user]\AppData\Local\LPub3D Software\LPub3D\libraries
Here you need to make sure the latest complete.zip is stored.
If you need non published parts available just copy/past those XX.dat files into the complete.zip file and restart LPub3D and voila the missing parts are visible and not anymore showing as ablack cube.