There has been a slight change since I posted the first message.
After posting the message, I changed the Selective Sync folders from "all selected" to "all unselected" to "all selected" - just to refresh the settings. Then, the blue sync symbol came up and a few thousand files started to sync , and in 10 minutes, it changed to the green tick with "Up to Date".
Currently, on the Dropbox icon next to Wifi, there is a green tick mark and "Up to Date". However, even after the apparent syncing, I only see a few folders (6 out of 15) right now.
None of the folders have any files visible in them. I see "This folder is empty."
When I manually type the path to a specific subfolder, I sometimes see a few (1 or 2 files) in it, when it is supposed to be having several files.