Sorry for my ignorance. I should told you hold the button after the Duo power up, not holding the button when reset occurred. What you have done gets the Duo into the factory reset mode, it clears all of WiFi credentials, device private key and overwrites your current sketch by a factory reset sketch.
But the odd thing is your Duo should stay in the listening mode after you performing a factory reset, while it didn’t. Please upload a simple blink sketch to the Duo to verify if the system firmware is broken or not.
Looking forward to you response.