Reading failed: A buffer is not big enough

[ear9mrn]

In my loop() I have the following:

void loop()
{


  if ( ! mfrc522.PICC_IsNewCardPresent() || ! mfrc522.PICC_ReadCardSerial() ){
    delay(30);
    return;
  }

  
  Serial.print(F("Card UID:"));
  for (byte i = 0; i < mfrc522.uid.size; i++) {
    if(mfrc522.uid.uidByte[i] < 0x10)
      Serial.print(F(" 0"));
    else
      Serial.print(F(" "));
    Serial.print(mfrc522.uid.uidByte[i], HEX);
  }
  Serial.println();

  readstatus = mfrc522.PCD_Authenticate(MFRC522::PICC_CMD_MF_AUTH_KEY_A, 4, &key, &(mfrc522.uid));
  if (readstatus != MFRC522::STATUS_OK) {
    Serial.print(F("Authentication failed: "));
    Serial.println(mfrc522.GetStatusCodeName(readstatus));
    
    //reset everything for the next card
    mfrc522.PCD_StopCrypto1();
    return;
  }
    
  byte buffer[18];
  readstatus = mfrc522.MIFARE_Read(block, buffer, &len);
      
  if (readstatus != MFRC522::STATUS_OK) {
    Serial.print(F("Reading failed: "));
    Serial.println(mfrc522.GetStatusCodeName(readstatus));
    
    //reset everything for the next card
    mfrc522.PCD_StopCrypto1();
    return;
  }

  //reset everything for the next card
  mfrc522.PCD_StopCrypto1();
  
  String value = "";
  for (uint8_t i = 0; i < 16; i++)
  {
      value += (char)buffer[i];
  }
  value.trim();
  Serial.println(value);
  
}

I am reading the content of block 4 of the card.

In general things work well but eventually (after about 20-30 reads) I get the following error.

Reading failed: The CRC_A does not match.

Which in itself is not a problem. Only issue is that on all following reads I get the this error:

Reading failed: A buffer is not big enough.

I then have to restart my Arduino (D1 mini). Is this a bug or a problem with how I have set the code up?

Thanks,

Pete.