Receiver cause restarting arduino

[simonik]

Hi,
I have an arduino ProMini 8MHz and I have a problem with the following code.
I receive data from time to time. But most of the time, Arduino is still being restarting. A registry dump is occurs, followed by a restart.
What could be the problem?
Thanks

void setup() {
Serial.begin(9600);
pinMode(6, OUTPUT);
digitalWrite(6, LOW);
Serial.println("LoRa Receiver");

LoRa.setSPIFrequency(2E6);
//LoRa.setPins(ss, reset, dio0);
LoRa.setPins(10,9);

if (!LoRa.begin(433E6)) {
Serial.println("Starting LoRa failed!");
while (1);
}
digitalWrite(6, HIGH);
delay(300);
digitalWrite(6, LOW);
LoRa.dumpRegisters(Serial);
}

void loop() {
// try to parse packet
int packetSize = LoRa.parsePacket();
if (packetSize) {
// received a packet
Serial.print("Received packet '");

// read packet
  String incoming = "";
while (LoRa.available()) {
//  Serial.print((char)LoRa.read());
    incoming += (char)LoRa.read();
}

  Serial.println("Message: " + incoming);
// print RSSI of packet
Serial.print("' with RSSI ");
Serial.println(LoRa.packetRssi());
Serial.println(incoming);
if(incoming.startsWith("zvonek"))
{
zahrajZnelku();
delay(200);
zahrajZnelku();
delay(200);
zahrajZnelku();
}

}
delay(100);
}