We are sorry to hear you are having trouble with the uploader. Are you using the Classic or DJI Specific workflow? Try the other one if you can.
Trying another computer would be good to help rule things out. We haven't heard of any issues with the new Mac OS version but is certainly possible.
The only reason a larger job would fail is because of increased resource usage. Maybe try closing some other applications/tabs to free things up. I doubt this is the problem though.
Keep us updated as to what you try and what works and what doesn't.