This last Thrusday, I suffered the same bug. I have a folder that contains all my company work that was selected and unselected from different devices.
Suddenly, the Dropbox deleted to me 600 file and 200 directory.
I raised a ticket with them and they said, that go to events. I went and I saw the massive deletion, and when I type, recovery this deletion, it does not work.
I am paying to the PRO account (1TB) to receive this service.
This is unbelievable.