icloudmacos
I am not using iCloud drive, and I am neither optimizing disk space with iCloud. But the disk utility app shows that I have 12.62 GB of "cancellable" disk space. I thought that this space was due to the fact that some files could be safely deleted from the disk because they're backed in iCloud. But why do I have "cancellable" storage if I am not using iCloud to optimize disk space?
It looks like iCloud Drive is still on:
Delete all files from it and then turn it off.
I see you've resolved your situation, but I wanted to write up a formal answer.
When you enable iCloud Drive, it has to go through a (very slow) process for each container of files before they show up. Each App Folder is one such container, and then all standalone files including Desktop and Documents goes in a generic container.
If you have lots of files (10+ GB can cause this to start happening) it can take hours (or days) before the files show up, even though they haven't even started downloading. In this time sync will not finish. If you have just enabled iCloud drive (either on a new computer or because you had turned it off) and you have a lot of files, trying to leave it plugged in etc. may help it go faster. Do not try to turn it off and then on, because it'll just start over.
I'm not sure why this happens, but it's the way it works right now. So if you don't see files after turning it on, let it sit for at least a day or two of having proper power and internet connection before trying other things.
Best Answer
This is a new feature in macOS Sierra called "purgeable space". Aside from files safely stored in iCloud (when the "Store in iCloud" option is enabled), purgeable space can also include cache and temporary files that are no longer required by the system.
It can also include other files that aren't entirely necessary, like iOS software updates, local Time Machine data, older email attachments, and others.