CocoaAsyncSocket sent UDP but no response

Question

infomation: I have a device on my local network, it is an UDP server and when I send "hello" to it I will get a "how are you" response, but I don't know the IP, so I have to send "hello" to each IP of my local network to find the device.

problem: when I send "hello" to my device,s IP directly, I get the response, but I send "hello" to each IP, I get no response most of the time( sometime I get a response)

some of my code:

//first create a instance of GCDAsyncUdpSocket

udpSocket = GCDAsyncUdpSocket(delegate: self, delegateQueue: DispatchQueue.global())
    do{
                log.debug("bind port")
                try self.udpSocket?.enableReusePort(true)
                try self.udpSocket?.bind(toPort: 0)
                udpBindedToPort = true
                try self.udpSocket?.beginReceiving()
            }catch {
                log.error("error")
                udpBindedToPort = false
                self.delegate?.findDeviceTimeout(0)
                return
            }

// this does not work

Async.background({[weak self] () in
            for i in 1...255 {
                let targetIP = ip_sub + ".\(i)"
                self?.send(Define.scanDeviceMessage, host: targetIP, tag: Define.scanDeviceTag)
            }
        })

//this works

Async.background({[weak self] () in
                let targetIP = "192.168.0.101"
                self?.send(Define.scanDeviceMessage, host: targetIP, tag: Define.scanDeviceTag)
        })

//the delegate

@objc func udpSocket(_ sock: GCDAsyncUdpSocket, didReceive data: Data, fromAddress address: Data, withFilterContext filterContext: Any?
    ) {
        print("UDP接收到数据 : \(String(data:data, encoding: String.Encoding.utf8))")
    }

thanks for your help, this drives me crazy, some times it works, but sometime not, and now it never works anymore