Doorbell 3 plus Can not connect to wifi

2 days ago, my 3 plus disconnected from wifi for no reason. I did not notice it until today but I can not connect it back no matter what I try. the door bell still power up normally, it will ring when plush bottom.I tried rebooting the door bell, router, and modem. The doorbell is 10 feet away from the router.I also tried reconnect the door bell, and the whith light always flashed right.tried hard reset and then reconnect, but still nothing.I feel like I have try every possible way.