I've had the same problem. I upgraded to Sierra and signed up for increased iCloud storage, then tried to dump 150GB of documents into it. It managed 32GB before hanging. I tried the advice further up the thread about stopping then restarting the sync with the same result.
I decided to try uploading in smaller chunks. On the Mac where the documents were originally stored I ensured that everything was in the iCloud Drive archive folder, then deleted everything from iCloud. I then moved the documents one folder at a time from the archive folder back to iCloud. It then became apparent that there were a few large "files" that it was having problems with. They were parallels virtual machines and sparse bundle disk images. Being pedantic, these are not really files but packages, nevertheless they seemed to overload the capacity of the iCloud uploader to cope. They were up to 21GB in size each.
I have kept these in a folder on my local hard drive. The rest of the upload is working fine now. It seems to cope with small sparse bundles (a few hundred MB).
The remote computer also seemed to struggle to download the files from iCloud, so when I am next in front of it I will try doing it a folder at a time.
It's pretty poor really. I have an online backup service that will happily store a 60GB sparse bundle without complaining. The initial upload took a very long time, due to its size (hundreds of GB - took weeks) but it completed in the time the internet connection would allow, without hanging. I would expect Apple to be able to manage this.