The RSSI values read with the ble connected device are not correctly correlated to the distance (swift core bluetooth)

I would like to monitor the rssi signal of the connected ble device (ble beacon) using the readRSSI () method of CBPeripheral but the values I get in the func peripheral (_ peripheral: CBPeripheral, didReadRSSI RSSI: NSNumber, error: Error?) Method do not change correctly moving the ble device away from / closer to the iPhone it is connected to. Instead, the Rssi values obtained for the same device in the func centralManager method (_ central: CBCentralManager, didDiscover peripheral: CBPeripheral, advertisementData: [String: Any], rssi RSSI: NSNumber) read during the peripheral scan are correctly correlated to the distance. The beacon chipset is NRF52810, the app uses swift 5 and iPhone software version is 15.4.1. Any suggestions on the cause of this abnormal behavior? Thanks for your help