Calling phpthumbon twice sometimes results in a 404 error. Why?

Question

MODX

Hello.
Here is my code:

$src = $modx->runSnippet('phpthumbon', [
    'input'   => $src,
    'options' => [
        'fltr' => ['size|2000|2000|0'],
    ]
]);  

$src = $modx->runSnippet('phpthumbon', [
    'input'   => $src,
    'options' => [
        'w'   => $w,
        'h'   => $h,
        'zc' => '1'
    ]
]);

I enlarge the pictures first and then crop them. This is done so that small images in height after processing by phpthumbon will be the same height as other images.
Because of this, sometimes pictures do not open for me - it just gives a 404 error. If we remove the snippet call with the fltr parameter, then everything works with a bang. What is the problem? How to fix it?