Can't save UUID field in PHP script iteration, Laravel, Postgres

I'm trying to fill already existing models with UUID. And every time it says that UUID is not unique! What a bloody hell! )))

  function unique_guid($model){
        $guid = com_create_guid();
        $table = $model->table;
        $db_table = Db::table($table);
        $req = $db_table->where("guid", strval($guid));
        $instance = $req->first();

        if(is_object($instance)){
            $guid = unique_guid($model);
            return;
        }else{
            try{
                $model->guid = $guid;
                $model->save();
                sleep(2);
                return $guid;
            }catch(PDOException $Exception){
                $guid = unique_guid($model);
            }

        }
    } 

It keeps circling in try/catch block and telling me that it is not unique, i checked and there is no record with genereted UUID. Also - it brokes at third-fourth iteration, and if i add sleep(5) it works longer - 10 iteration and then brokes. What in the world can it be? Laravel 5.5, Postgres 9

via Chebli Mohamed