The online counter only sees two, what's the problem?

Question

PHP

There is a counter code

<?php
session_start();
//выделяем уникальный идентификатор сессии
$id = session_id();

if ($id!="") {
//текущее время
$CurrentTime = time();
//через какое время сессии удаляются
$LastTime = time() - 600;
//файл, в котором храним идентификаторы и время
$base = "session.txt";

$file = file($base);
$k = 0;
for ($i = 0; $i < sizeof($file); $i++) {
$line = explode("|", $file[$i]);
if ($line[1] > $LastTime) {
$ResFile[$k] = $file[$i];
$k++;
}
}

for ($i = 0; $i<sizeof($ResFile); $i++) {
$line = explode("|", $ResFile[$i]);
if ($line[0]==$id) {
$line[1] = trim($CurrentTime)."\n";
$is_sid_in_file = 1;
}
$line = implode("|", $line); $ResFile[$i] = $line;
}

$fp = fopen($base, "w");
for ($i = 0; $i<sizeof($ResFile); $i++) { fputs($fp, $ResFile[$i]); }
fclose($fp);

if (!$is_sid_in_file) {
$fp = fopen($base, "a-");
$line = $id."|".$CurrentTime."\n";
fputs($fp, $line);
fclose($fp);
}
}
?>

But the problem is, when displaying on the page, there are always 2 online, in session.txt it enters only two, and no matter how many people are on the site, there are always two!
What could be the problem?
Or does anyone have other examples of simple counters?
I will be grateful :)