This snippet will return chunks in a random order.

randomChunk.php

<?php
//-----------------------------------------------------------
//  randomChunk
//-----------------------------------------------------------
/*
 * @author: Steeve from lawebfabric
 * @website: http://www.lawebfabric.com
 * @tutorial modx website: http://www.tutocms.fr/
 * 
 * Created on: 08/10/18
 *
 * DESCRIPTION
 * This snippet will return chunks in a random order.
 *
 * PROPERTIES:
 * &chunks string of all name chunks comma separated. Required!
 * &howManyChunks integer. If not define all chunks will be displayed.
 *
 * USAGE:
 * [[!randomChunk? &chunks=`firstChunkName,secondChunkName,nameofchunk,anotherChunk` &howManyChunks=`2`]]
 *
 */

$chunks         = $modx->getOption('chunks', $scriptProperties);
$howManyChunks  = $modx->getOption('howManyChunks', $scriptProperties);
$output         = false;

$chunksArray    = explode(",", $chunks);
$totalChunks    = count($chunksArray);

// ERRORS
if (!isset($scriptProperties['chunks'])) {
    	$modx->log(modX::LOG_LEVEL_ERROR, '[randomChunk] missing required properties &chunks!');
    return;
}
if (isset($scriptProperties['howManyChunks']) && $howManyChunks > $totalChunks) {
    	$modx->log(modX::LOG_LEVEL_ERROR, '[randomChunk] howManyChunks properties is bigger than the number of chunks');
    return;
} 

// rand the array (keep assoc key => value)
function arrayKeyShuffle(&$array) {
    if(!is_array($array) || empty($array)) {
        return false;
    }
    $tmp = array();
    foreach($array as $key => $value) {
        $tmp[] = array('k' => $key, 'v' => $value);
    }
    shuffle($tmp);
    $array = array();
    foreach($tmp as $entry) {
        $array[$entry['k']] = $entry['v'];
    }
    return true;
}

// shuffle chuks array
arrayKeyShuffle($chunksArray);

if(isset($scriptProperties['howManyChunks'])) {
    
    $i=0;
    $rand_keys = array_rand($chunksArray, $howManyChunks);
    
    // retunr number of chunks asked in howManyChunks properties in a random order
    while ($i < $howManyChunks) {
        $output .= $modx->getChunk($chunksArray[$rand_keys[$i]],array());
        $i++;
    }
    
}else{
    
    // return random all chunks
    foreach ($chunksArray as $chunk) {
        $output .= $modx->getChunk($chunk,array());   
    }
    
}

return $output;