Exception occurred when creating MZContentProviderUpload for provider. (1004)

It seems like a temporary issue with apple. Trying few times to send worked and the upload was successful.

For me just log out on Web iTunesConect / AppsoreConnect portal.

Quit Xcode (if Possible restart) and then upload the build.

If you close all the other app and upload build in sylo makes a job easy.

Also using the "Application Loader" is a Good Solution!

I was facing same issue. In my case I tried to login another Apple Developer account via Safari. I solved this by doing:

Logout the account from Xcode and login again. It works successfully for me. No need to generate build again.

I was getting this error many times during 3 hours. Sometimes along with other errors with it.

What helped: re-loginning toitunesconnect and restarting Mac after that. Build has uploaded from 1st attempt.

I got this error when I log in a different account in another app(iBook log in as my personal account). I solved this by re-login in xCode, re-archive the app, upload again.

A restart of macOS fixed this issue for me. Restarting Xcode and signing out of iTunes Connect didn't help. Also, no need to rebuild again. After the restart the previous build uploaded just fine on the first attempt.