I’m using Kicad professionaly for more than one year now. I’m very pleased with it.
But sometimes, I have to work in paralell with a mechanical engineer so I have to export a 3D step with the most space consuming parts.
Regularly, when I open a board and check the 3D vizualisation, some user-added parts are missing. When I check in the footprint parameters, it’s like I just added a footprint alone and no 3D part is referenced.
A thing which can provide explanations is that I work on this project on an USB key and sometimes open the project on a different PC. But I checked that everything is linked with relative paths.
3d models are not really managed. The footprint points to the files directly.
But you can use environment variables.
I am not sure what you mean with using relative paths. If i remember correctly entering relative paths into footprint settings will mean it is relative to the KISYS3DMOD path variable.