Program: 29270
Project: 29270
Buggy source:
private String _encode(long... numbers){
  int numberHashInt=0;
  for (int i=0; i < numbers.length; i++) {
    numberHashInt+=(numbers[i] % (i + 100));
  }
  String alphabet=this.alphabet;
  char ret=alphabet.charAt(numberHashInt % alphabet.length());
  long num;
  int sepsIndex, guardIndex;
  String buffer;
  StringBuilder ret_strB=new StringBuilder(minHashLength);
  ret_strB.append(ret);
  char guard;
  for (int i=0; i < numbers.length; i++) {
    num=numbers[i];
    buffer=ret + this.salt + alphabet;
    alphabet=Hashids.consistentShuffle(alphabet,buffer.substring(0,alphabet.length()));
    String last=Hashids.hash(num,alphabet);
    ret_strB.append(last);
    if (i + 1 < numbers.length) {
      num%=((int)last.charAt(0) + i);
      sepsIndex=(int)(num % this.seps.length());
      ret_strB.append(this.seps.charAt(sepsIndex));
    }
  }
  String ret_str=ret_strB.toString();
  if (ret_str.length() < this.minHashLength) {
    guardIndex=(numberHashInt + (int)(ret_str.charAt(0))) % this.guards.length();
    guard=this.guards.charAt(guardIndex);
    ret_str=guard + ret_str;
    if (ret_str.length() < this.minHashLength) {
      guardIndex=(numberHashInt + (int)(ret_str.charAt(2))) % this.guards.length();
      guard=this.guards.charAt(guardIndex);
      ret_str+=guard;
    }
  }
  int halfLen=alphabet.length() / 2;
  while (ret_str.length() < this.minHashLength) {
    alphabet=Hashids.consistentShuffle(alphabet,alphabet);
    ret_str=alphabet.substring(halfLen) + ret_str + alphabet.substring(0,halfLen);
    int excess=ret_str.length() - this.minHashLength;
    if (excess > 0) {
      int start_pos=excess / 2;
      ret_str=ret_str.substring(start_pos,start_pos + this.minHashLength);
    }
  }
  return ret_str;
}

Fixed version (ground truth):
private String _encode(long... numbers){
  long numberHashInt=0;
  for (int i=0; i < numbers.length; i++) {
    numberHashInt+=(numbers[i] % (i + 100));
  }
  String alphabet=this.alphabet;
  char ret=alphabet.charAt((int)(numberHashInt % alphabet.length()));
  long num;
  long sepsIndex, guardIndex;
  String buffer;
  StringBuilder ret_strB=new StringBuilder(minHashLength);
  ret_strB.append(ret);
  char guard;
  for (int i=0; i < numbers.length; i++) {
    num=numbers[i];
    buffer=ret + this.salt + alphabet;
    alphabet=Hashids.consistentShuffle(alphabet,buffer.substring(0,alphabet.length()));
    String last=Hashids.hash(num,alphabet);
    ret_strB.append(last);
    if (i + 1 < numbers.length) {
      num%=((int)last.charAt(0) + i);
      sepsIndex=(int)(num % this.seps.length());
      ret_strB.append(this.seps.charAt((int)sepsIndex));
    }
  }
  String ret_str=ret_strB.toString();
  if (ret_str.length() < this.minHashLength) {
    guardIndex=(numberHashInt + (int)(ret_str.charAt(0))) % this.guards.length();
    guard=this.guards.charAt((int)guardIndex);
    ret_str=guard + ret_str;
    if (ret_str.length() < this.minHashLength) {
      guardIndex=(numberHashInt + (int)(ret_str.charAt(2))) % this.guards.length();
      guard=this.guards.charAt((int)guardIndex);
      ret_str+=guard;
    }
  }
  int halfLen=alphabet.length() / 2;
  while (ret_str.length() < this.minHashLength) {
    alphabet=Hashids.consistentShuffle(alphabet,alphabet);
    ret_str=alphabet.substring(halfLen) + ret_str + alphabet.substring(0,halfLen);
    int excess=ret_str.length() - this.minHashLength;
    if (excess > 0) {
      int start_pos=excess / 2;
      ret_str=ret_str.substring(start_pos,start_pos + this.minHashLength);
    }
  }
  return ret_str;
}