Exception raised when trying to perform a new ModBus connection after a connection loss

/**
 * This slot is connected to the timeout event of the QTimer configured in the
 * constructor of the class.
 *
 * It is used to read periodically the new values of the input registers of
 * the board or to reset the Modbus connection in case of a false reply
 * timeout which can occurs with some RS485 USB controllers.
 *
 * If a connection reset is requested after the first reply, we assume there is
 * no board connected on the current serial port and we close the
 * connection.
 */
void Nitroxychrom::readAllInputRegisters() {
    if (!resetConnection) {
        QModbusDataUnit request = QModbusDataUnit(QModbusDataUnit::InputRegisters, 0, MODBUS_INPUT_REG_NUMBER);
        QModbusReply *reply = modbusMaster->sendReadRequest(request, 2);

        if (!reply->isFinished()) {
            connect(reply, &QModbusReply::finished, this, &Nitroxychrom::replyReady);
        } else {
            parseReply(reply);
        }
    } else {
        resetConnection = false;

        timer->stop();
        modbusMaster->disconnectDevice();
        delete modbusMaster;
        modbusMaster = nullptr;

        if (firstRead) {
            // There is no connected CPREG-N2 board or it doesn't reply the proper data
            ui->serialPortListBox->setEnabled(true);
            ui->serialPortListRefreshButton->setEnabled(true);
            ui->connectButton->setText(tr("Connect"));

            setConnectionState(ConnectionState::Error);
        } else {
            // Performing the new connection
            modbusMaster = new QModbusRtuSerialMaster(this);
            modbusMaster->setConnectionParameter(QModbusDevice::SerialPortNameParameter, ui->serialPortListBox->currentText());
            modbusMaster->setConnectionParameter(QModbusDevice::SerialParityParameter, QSerialPort::NoParity);
            modbusMaster->setConnectionParameter(QModbusDevice::SerialBaudRateParameter, QSerialPort::Baud9600);
            modbusMaster->setConnectionParameter(QModbusDevice::SerialDataBitsParameter, QSerialPort::Data8);
            modbusMaster->setConnectionParameter(QModbusDevice::SerialStopBitsParameter, QSerialPort::OneStop);
            modbusMaster->setTimeout(1000);
            modbusMaster->setNumberOfRetries(3);

            connect(modbusMaster, &QModbusRtuSerialMaster::stateChanged, this, &Nitroxychrom::modbusStateChanged);

            if (!modbusMaster->connectDevice()) {
                delete modbusMaster;
                modbusMaster = nullptr;

                ui->serialPortListBox->setEnabled(true);
                ui->serialPortListRefreshButton->setEnabled(true);
                ui->connectButton->setText(tr("Connect"));

                setConnectionState(ConnectionState::TimeOut);
            }
        }
    }
}