I've been having the same issue on and off for months now. Fully upgraded to newest MAC OS. Today it happened within the same folder as I was changing sync to "online only" for a few files I don't need access to locally. Within the same folder, the first few gave me the Dropbox options for sync, and then suddenly/randomly, those options fully disappeared and nothing I've tried has gotten them back again. I'm about to force quit Finder, as that has worked in the past. But it's a very random issue that keeps happening. Definitely needs the attention of both Apple and Dropbox developers to resolve, as it wastes a LOT of time on admin/housekeeping issues. Time that SHOULD be spent actually getting real work done.