Program: 101853
Project: 101853
Buggy source:
public boolean checkYAxis(Player player,Distance distance){
  if (distance.getYDifference() > 400) {
    return false;
  }
  if (!isMovingExempt(player) && !Utilities.isOnLadder(player) && !player.isInsideVehicle()) {
    double y1=player.getLocation().getY();
    String name=player.getName();
    if (!lastYcoord.containsKey(name) || !lastYtime.containsKey(name) || !yAxisLastViolation.containsKey(name)|| !yAxisLastViolation.containsKey(name)) {
      lastYcoord.put(name,y1);
      yAxisViolations.put(name,0);
      yAxisLastViolation.put(name,0L);
      lastYtime.put(name,System.currentTimeMillis());
    }
 else {
      if (y1 > lastYcoord.get(name) && yAxisViolations.get(name) > Y_MAXVIOLATIONS && (System.currentTimeMillis() - yAxisLastViolation.get(name)) < Y_MAXVIOTIME) {
        Location g=player.getLocation();
        g.setY(lastYcoord.get(name));
        player.sendMessage(ChatColor.RED + "String_Node_Str");
        yAxisViolations.put(name,yAxisViolations.get(name) + 1);
        yAxisLastViolation.put(name,System.currentTimeMillis());
        if (g.getBlock().getTypeId() == 0) {
          player.teleport(g);
        }
        return true;
      }
 else {
        if (yAxisViolations.get(name) > Y_MAXVIOLATIONS && (System.currentTimeMillis() - yAxisLastViolation.get(name)) > Y_MAXVIOTIME) {
          yAxisViolations.put(name,0);
          yAxisLastViolation.put(name,0L);
        }
      }
      if ((y1 - lastYcoord.get(name)) > Y_MAXDIFF && (System.currentTimeMillis() - lastYtime.get(name)) < Y_TIME) {
        Location g=player.getLocation();
        g.setY(lastYcoord.get(name));
        yAxisViolations.put(name,yAxisViolations.get(name) + 1);
        yAxisLastViolation.put(name,System.currentTimeMillis());
        if (g.getBlock().getTypeId() == 0) {
          player.teleport(g);
        }
        return true;
      }
 else {
        if ((y1 - lastYcoord.get(name)) > Y_MAXDIFF + 1 || (System.currentTimeMillis() - lastYtime.get(name)) > Y_TIME) {
          lastYtime.put(name,System.currentTimeMillis());
          lastYcoord.put(name,y1);
        }
      }
    }
  }
  return false;
}

Fixed version (ground truth):
public boolean checkYAxis(Player player,Distance distance){
  if (distance.getYDifference() > 400) {
    return false;
  }
  if (!isMovingExempt(player) && !Utilities.isOnLadder(player) && !player.isInsideVehicle()&& !Utilities.isInWater(player)) {
    double y1=player.getLocation().getY();
    String name=player.getName();
    if (!lastYcoord.containsKey(name) || !lastYtime.containsKey(name) || !yAxisLastViolation.containsKey(name)|| !yAxisLastViolation.containsKey(name)) {
      lastYcoord.put(name,y1);
      yAxisViolations.put(name,0);
      yAxisLastViolation.put(name,0L);
      lastYtime.put(name,System.currentTimeMillis());
    }
 else {
      if (y1 > lastYcoord.get(name) && yAxisViolations.get(name) > Y_MAXVIOLATIONS && (System.currentTimeMillis() - yAxisLastViolation.get(name)) < Y_MAXVIOTIME) {
        Location g=player.getLocation();
        g.setY(lastYcoord.get(name));
        player.sendMessage(ChatColor.RED + "String_Node_Str");
        yAxisViolations.put(name,yAxisViolations.get(name) + 1);
        yAxisLastViolation.put(name,System.currentTimeMillis());
        if (g.getBlock().getTypeId() == 0) {
          player.teleport(g);
        }
        return true;
      }
 else {
        if (yAxisViolations.get(name) > Y_MAXVIOLATIONS && (System.currentTimeMillis() - yAxisLastViolation.get(name)) > Y_MAXVIOTIME) {
          yAxisViolations.put(name,0);
          yAxisLastViolation.put(name,0L);
        }
      }
      if ((y1 - lastYcoord.get(name)) > Y_MAXDIFF && (System.currentTimeMillis() - lastYtime.get(name)) < Y_TIME) {
        Location g=player.getLocation();
        g.setY(lastYcoord.get(name));
        yAxisViolations.put(name,yAxisViolations.get(name) + 1);
        yAxisLastViolation.put(name,System.currentTimeMillis());
        if (g.getBlock().getTypeId() == 0) {
          player.teleport(g);
        }
        return true;
      }
 else {
        if ((y1 - lastYcoord.get(name)) > Y_MAXDIFF + 1 || (System.currentTimeMillis() - lastYtime.get(name)) > Y_TIME) {
          lastYtime.put(name,System.currentTimeMillis());
          lastYcoord.put(name,y1);
        }
      }
    }
  }
  return false;
}