I aggressively use selective sync, and have since as long as I can remember yet I haven't got an email like this, so it may only affect specific users.
It appears the circumstance is more specific than simply using selective sync.
> This problem occurred when the Dropbox desktop application shut down or restarted while users were applying Selective Sync settings.
So, you must be in the midst of applying selective sync settings while the app shuts down or restarts. Although I'm not sure what they mean when they say, "while users were applying selective sync settings." I'm not sure if this means:
A) Changes made in the selection dialog box, but not committed (by clicking OK).
or
B) Changes committed, but still syncing.
The former is an edge case, the later, not so much.
