Hi,
I have had this issue several times, when I'm using dropbox in windows explorer and I want to make my dropbox files only available online but by mistake I click on the option to make all files available offline and there is no way to cancel the process.
This is very annoying because I don't want to sync almost 3TB to my computer, often I don't even have enough space to do so, but dropbox keeps trying and taking forever to sync until I can make those files only available onlline again, so the only solution is to pause the synchronization and completely uninstall Dropbox, reinstall it again and wait for it to check everything once again, which is also a process that takes a good amount of time.
Please add an option to fully cancel a sync because I'm really thinking of cancelling my subscription at this point, it is very annoying and this problem has been known for a while already. Also why do you set the option to make all files available offline right next to the option to make them only available online? That makes it very easy to click the wrong one by mistake.