If you have a zip file containing files with special characters in their names referencing each other, then you might run into problems when translating them using the Model Derivative service. This issue is not specific to this service.
If you have a zip file and for some reason, the file names were not encoded in a way that they can be unzipped correctly on any platform then the necessary files won't be found, since they won't have the correct name. Find some suggestions here (though it's regarding the Design Automation service the suggestions could be applied here too): https://stackoverflow.com/a/66569755/4654233
When I tried to zip my files with the default app on Windows, it could not even deal with them:
If I zipped them up with the default app on macOS then tried to unzip them using the default app on Windows, I ended up with these files:
If I passed this zip file to the Model Derivative service, the translation failed - i.e. the model was empty - see picture on top.
If I used 7-zip to zip up the files then after unzipping them (both 7-zip and default app worked) I ended up with the correct file names in the unzipped folder, and this zip file worked on the Model Derivative service as well.