Still had the same error. Cut down my world from 3GB to 780MB and files from 1100 to 300. Stops at error 504 or 401. Once, after an error-out, I was able to get my world with about half of my existing chunks regenerated (buildings half gone). Uploading with a 30MB world with 50 files works fine. It’s kinda frustrating.
Reduced my world size further to 331MB and 193 files. Still no luck.