VB.NET SerialPort 串口DataReceived事件，超过五十分钟后无法触发

Private Sub btnKeiRyo_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnv_nJ.Click
If SerialPortHaKaRi IsNot Nothing Then
If SerialPortHaKaRi.IsOpen = True Then
SerialPortHaKaRi.Close()
End If
If SerialPortHaKaRi.IsOpen = False Then
SerialPortHaKaRi.Open()
'TCY
SerialPortHaKaRi.ReceivedBytesThreshold = 1
End If

SerialPortHaKaRi.WriteLine(haKaRi_temp)
End If
End Sub

Private Sub SerialPort1_DataReceived(ByVal sender As Object, ByVal e As System.IO.Ports.SerialDataReceivedEventArgs) Handles SerialPortHaKaRi.DataReceived
Dim strRecvData As String = ""
strRecvData = SerialPortHaKaRi.ReadExisting
Call disPlayComData(strRecvData)

If SerialPortHaKaRi IsNot Nothing Then
If SerialPortHaKaRi.IsOpen = True Then
SerialPortHaKaRi.Close()
End If
End If
End Sub

但是把程序重新启动，就又能触发了。
感觉时间长之后，程序好像变得慢了
Delegate Sub callback(ByVal strT As String) '定义委托

Sub showString(ByVal comdata As String) '显示结果
strHaKaRi_TEMP = comdata
F_ハカリ_设定()
End Sub

Sub disPlayComData(ByVal strTmp As String) '判定是否为跨线程
If Me.lbl入力値.InvokeRequired Then
Dim d As New callback(AddressOf showString)
Me.Invoke(d, New Object() {strTmp})
Else
strHaKaRi_TEMP = strTmp
F_ハカリ_设定()
End If
End Sub

如能解决，可加分啊。帮帮忙~

这么厉害。还真的是usb转的232。但是直接插在COM口上。还是不好使啊。我在试一遍。不能理解的是，为什么只有重启程序才能触发。不然就一直不好使了