A folder was shared by the owner with five people. It contains a spreadsheet that is routinely updated. For more than a year, we have received email notifications when the owner made changes. Now those emails have stopped for some reason. Owner hasn't made changes to her settings, either have recipients. I can go into Dropbox, open folder, and see the Activity pane at the right telling me she's edited the document. But we're no longer receiving the email notifications. How do we fix this?