To be honest I don't have any Tiles and haven't used them. They may take a while to switch back to advertising or stop advertising after a while unless a button is pressed? I'm not sure.
Are you checking the 'Latest Beacons Seen' part of the presence server? Try to keep the Tile close (just a few feet) from one of the detectors and see if they show up with a very strong signal.
Is your detector picking up other devices?