It's been happening for several weeks: I attempt to use the Dropbox app (v. 222.2.2, currently) on my Android phone (v. 9, kernel 4.9.112-15805288) to upload photos and it stays on "Waiting to upload...".
I have gone through all the solutions I've found on the forums (clearing cache, logging out and back in, uninstalling and reinstalling the app) but the problem persists.
Transferring data between my mobile device and the central server is one of the main uses for my account (and why I'm paying for the service, which I am thinking of discontinuing if the issues persist--don't get me started on how each update to the web-client makes it more confusing and unusable).