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:

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';