Is your computer running MacOS or Windows?
If I had read the earlier posts more carefully, I would have realized you had said you are on a Mac. My apologies.
Two things you can check:
Under System Preferences → Apple ID → iCloud make sure “Optimize Mac Storage” is off
Also under the Dropbox Preferences menu → Sync make sure Smart Sync is set to not “Save hard drive space automatically”.
Either (or both) of these could cause issues.