readCharacteristic's monitor return same data three times

[deepseeksss]

i have a peripheral run at my phone with android gatt server api implement as a echo server

but every time send some data to the peripheral, central received the same data three times with monitor's onListen callback

i send back the data at peripheral as follows:

_characteristicRead?.value = data
_bluetoothGattServer?.notifyCharacteristicChanged(device, _characteristicRead, false)