Some OBD/ELM327 diagnostic tools are with led indicators. Generally one is for powerstatus, one is for OBD/ECU, and the other is for communication mode (USB,Bluetooth or WIFI).
The indicators should be different in colors and they will help you to know the real time status, if they do not work, you have to check the connection and setting of the device or software.
If the OBD indicator keeps flashing, means the diagnostic tool do not work stably. There is no flash if the OBD diagnostic tool works in good condition.