Something went wrong with the upload. Please try again.

I have the exacly problem and my account is suposed to be unlimited.  I also a developer, and some of my client is with same problem. 

And it doesn't matter if the upload is done via ftp, web, desktop app, mobile app, using the box's own cloud migration system, or another api.

I'm having exact same issue since 3 days ago. I upload via rclone and all uploads keep failing and going back from 100% done to 0% done and uploading again.
Tried uploading via browser and getting error like OP. I also have unlimited account.

Hi Kevin, 

Welcome to Box Community and glad to help! 

It appears that you're already working with the Product Support team to address your issue. Please keep an eye out and we'll stay in touch. 

Thanks for posting!  

No. They are not helping me.
They closed my ticket with no response.
How strange that.

in airexplorer I get sales error 429 too many requests

practically all box accounts have this problem. I believe box is out of disk space, and that's why it's happening to at least everyone I know who uses box business.

looks like issue is gone, lasted 5 days.

I'm a developer, and I manage 30 other box accounts, from different  planas, like business plans, Business Plus, and enterprise, and everyone has the same problem.
Since the 31st, no one has been able to send anything. Some of these people received email, some didn't, and with everyone it's the same problem.
You say to write to your sales service but even my customers who have the enterprise plan are having the same limitation.
Are you out of disk space for customers? That's what I'm seeing on all the forums, because it's not my account, or the account of my 30 clients who are having this problem. I've seen reports of more than 1000 customers with the same problem, and what everyone is thinking is that box.com is out of disk space for customers, so no one can upload anymore.

aand it lasted 8 days. Issue is back.