Hey All,
Originally I had the issue, that my dropbox doesn't sync properly to one of my machines: a Windows 10 PC. It looks as if one of my folders is selectively synced (90% of its contents are unavailable on my machine), while no selective sync is set up in the preferences - and the missing folders do show up in the relevant preference pane.
While looking for a solution, I tried to see if setting some files offline or online via the right-click context-menu commands in Windows Explorer helps, but it didn't. I have the latest version of the desktop app installed.