Just a quick demo highlighting that PHP doesn't preserve same-value keys order while running an associative sort

associative-sort.php

<?php

$a = [];
$threshold = 120;

while (count($a) < 400) {
    $v = count($a) > $threshold ? 'a' : 'b';
    $a[] = $v;
}

asort($a);
// keys are preserved but their order within keys containing the same value is not.
var_dump($a);
die;