I think all the files are usable, I have tested myself and found no problems. Maybe the problems come from your setup, but if you give us more information we can try to fix it:
I have downloaded the repo, and opened the file with LibreCAD, I haven't found any problem. The problem may exist and other users have reported similar issues, but please give us more information about the error so we can try to fix it.
Currently we do not provide .step files, only the FreeCAD and fabrication (.dxf, .stl) files. I consider FreeCAD files usable, since you can open them in any platform and export them to many other formats. I have also taken my time to open a part in FreeCAD, export to .step and then open the file (in both FreeCAD and Adobe Fusion 360) and haven't found any problem with that. If you give us more information about this issue maybe we can fix it.
good luck trying to convert this file to something usable