Recently I discovered a similar problem.
I have a multi-story residential project created on Mac, completed on Windows using the localized GS Dutch library 12 - no custom library parts included.
Saving the file to .pla, transfer to Mac, everything opens fine >
directly from the archive <!.
However, in the open dialogs both on Mac and Windows, exporting the objects into a separate library folder, none of the objects get mounted. I checked this library folder and it's empty! I only have textures available !?!
Back to Mac, open the file with the original library, saving to .pla and everything is loading fine
The one thing strange, If I try the extracted file on Mac with the original library loaded, none of the objects are altered and I have various error messages about wrong parameters...