Updated files not replacing/overwriting

The plugin has been working fine for years but I recently updated and files no longer seem to be overwriting/replacing when they have been updated.

Deleting a file in dropbox then running the backup process again does correctly upload the file back to dropbox. However if I subsequently make a change to that file then run the backup, it doesnt get replaced so the OLD version of that file is on dropbox (e.g. its not an up to date backup at all).

Any ideas? It is a bit frustrating.

Thanks