Thank you, Daphne. I had no idea I was on a beta version of the Mac sync client. I'll downgrade to the stable branch and see if things improve.
I think it was right to make this thread as solved, after all it was an OS beta release.
I've now updated to macOS Catalina Beta 2 and it appears that whatever was causing dropbox to not automatically sync has disappeared as I'm able to create/edit files in my dropbox folder and they do get uploaded.
Only issue on macOS Catalina Beta 2 is the dropbox app periodically crashes but restarts straight away, which causes is to start sync'in... so still better than Beta 1, ha!
Am using MacOS 10.15 (19A487m) and am getting a "Can't access dropbox folder" error. It appears to be sync'ing only intermittently. I'm using Dropbox v75.4.141.
Dropbox does not yet support macOS Catalina (10.15) and won't until its final, stable release. You may be able to install Dropbox on it but you're bound to run into issues until Dropbox officially supports it.
I would uninstall and reinstall it... Catalina has new file access permissions for each time an app wants to access somewhere it hasn't before... failing that check the permissions for dropbox under system preferences and make sure it has full disk access.
I carried out your two suggestions sequentially, each time rebooting my computer. Neither worked by itself nor in combination.
So, I went back in to "Full Disk Access" list and removed Dropbox from the approved list. As an aside, Google Drive was unaffected by the current Catalina build and did not require Full Disk Access.
I examined the list of apps under "Accessibility" and Dropbox was enabled for that function.
Thanks so much for your suggestions, though. In the process, I did re-learn that uninstalling and re-installing is in fact different from merely deleting the desktop app and re-installing.
I'm running Dropbox beta build v76.3.110 on the 2nd beta of Catalina and as soon as I change a file I can see dropbox syncing .
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Solved! : See solution