There are several reasons your reports might be empty.
1. Have the guards been patrolling?
Do a clocking round yourself to confirm if this is the problem
2. Is the unit communicating with the server?
Check the unit on site, is the green light on indicating that the unit is functioning correctly. If not, check the troubleshooting guide.
3. Are the guards uploading correctly?
Take a look at the Magcell downloading guide to see exactly how it needs to be done. Ensure the green light is on before downloading. Place the baton on the unit and only remove it when the middle light starts flashing(not when it comes on). If the bottom light flashes the upload was unsuccessful or the baton was empty.