Uploading of Desktop and Documents to iCloud hasn’t worked for me for months (macOS 10.12).

I have now started from scratch with a brand-new install, and am trying to sync just ~70MB of files that are sitting on the desktop.

It’s been stuck on “77.8MB of 77.8MB” for 3 days.

Why does this happen, and how can I fix it?

I’ve looked at possible solutions (like logging out etc.), but this is a fresh install, shouldn’t it just work?