SOLVED! (Brute force style)
The error message in the log complained about /home/nobody/Downloads
This is a directory found in the settings.json file under 'incomplete-dir:'
I changed 'incomplete-dir-enabled' to "false" and the download works fine.
Granted, I won't be able to use the "incomplete" functionality but frankly IDGAF so I won't investigate why transmission aren't allowed to create /home/nobody/Downloads.