В конце концов разобрался. И все стало работать. Необходимо путь в источнике файлов делать некешируемым [[!migxResourceMediaPath? &pathTpl=assets/images/{id}/]] Код процессора который я написал для себя: <?php

require_once MODX_CORE_PATH .'components/migx/model/migx/migx.class.php';

class GetDataMIGxProcessor extends modProcessor{

public function initialize(){
    
    $this->setDefaultProperties(array(
        'tvname'        =>  '',
        'id'            =>  0, //id ресурса
        'randomize'     =>  0,
        'limit'         =>  0,
        'nameMS'	    => 	'' //имя MediaSource
    ));
    
    return parent::initialize();
}

private function GetPath(){
$this->modx->setPlaceholder('docid', $this->getProperty('id'));
    $source = $this->modx->getObject('modMediaSource', array('name'=>$this->getProperty('nameMS')));
    
    $this->modx->resource = $this->modx->getObject('modResource', $this->getProperty('id'));

    $source->initialize(); 
    $value = $source->getBaseUrl();
    
    //unset($source);
    return  $value;
    
    
}

private function FindFields(xPDOObject $object)
{   
    
    $migx = new MIGX($this->modx);

    $config_r = $object->get('input_properties');
    $config = $config_r['configs'];
    //

    $q = $this->modx->getObject('migxConfig', array('name'=>$config));
    $data = $this->modx->fromJSON(trim($q->get('formtabs'),  '[]'));

    $res_field = array();

    foreach($data['fields'] as $field){
        if ($field['inputTVtype'] == 'image' || $field['inputTVtype'] == 'file')
            $res_field = $res_field + array($field['field']);
        }
    
    
    unset($migx);
    
    return $res_field;
}

private function GetTVValue($path){
    $q = $this->modx->newQuery('modTemplateVar');
    $q->innerJoin('modTemplateVarResource', 'v', 'v.tmplvarid = modTemplateVar.id');
    $q->where(array('modTemplateVar.name'=> $this->getProperty('tvname'), 'v.contentid' => $this->getProperty('id')));
    $q->select(array('v.*, modTemplateVar.input_properties'));
        
    $q->prepare();

    $tv = $this->modx->getObject('modTemplateVar', $q);

    $keys = $this->FindFields($tv);
    $object = $this->modx->fromJSON($tv->get('value'));
    
    $list = array();
    $index = 0;
    
    if ($this->getProperty('randomize') != 0)
        shuffle($object);
    
    foreach ($object as $tv){

        for ($i = 0; count($keys) > $i; $i++){
            if(array_key_exists($keys[$i], $tv)){
            
                $tv[$keys[$i]] = implode("", array($path, $tv[$keys[$i]]));
            }
        }
        array_push($list, $tv);
        $index++;
        
        if ($this->getProperty('limit') != 0 && $this->getProperty('limit') == $index)
            break;
    }
    
    //$list['count'] = $index; 

    return array("count" => $index, "object" => $list);
}

public function process(){
    $path = $this->GetPath();
    $tv_objects = $this->GetTVValue($path);
    
    return $tv_objects;
}

}

return 'GetDataMIGxProcessor';