On Gen 3 devices (Argon, Boron, B-Series SoM, and Tracker) running Device OS 3.x or earlier, it is necessary to mark setup done. This can be done using the Particle CLI:

particle usb setup-done

• The device should be in a normal operating mode to use this command. It cannot be used in DFU mode (blinking yellow).
• If you do not mark setup done, the device will boot into listening mode (blinking dark blue).
• Starting with Device OS 4.x, this step is no longer necessary.