Fatal error: Uncaught exception ‘SmartyException’ with message ‘Unable to load template snippet’

Hi guys,
I’ve made a plugin to extend the buttons on the orders listing page in the administration.
As soon as I load the Backend I get a error box with the following error:

The content of the backend/arv_extend_order/view/list/filter.js reads as follows:

//{block name="backend/order/view/list/filter"}
// {$smarty.block.parent}
Ext.define('Shopware.apps.ArvExtendOrder.view.list.Filter', {
    override: 'Shopware.apps.Order.view.list.Filter',
    createFilterButtons: function () {
       // shortend for readability reasons

If I remove the 2nd line in question, then I get a different error message:

<br />
<b>Fatal error</b>:  Uncaught SmartyException: Unable to load template snippet 'backend/arv_extend_order/controller/arv_order_controller.js' in 'backend/order/app.js|backend/arv_extend_order/app.js' in /var/www/html/engine/Library/Smarty/sysplugins/smarty_internal_templatebase.php:127

The content of the backend/arv_extend_order/controller/arv_order_controller.js:

//{block name="backend/order/controller/filter"}
// {$smarty.block.parent}
Ext.define('Shopware.apps.ArvExtendOrder.controller.Filter', {
    override: 'Shopware.apps.Order.controller.Filter',
    init: function () {
       // shortend for readability reasons

The content of the backend/arv_extend_order/app.js:

//{block name="backend/order/application"}
// {$smarty.block.parent}
// {include file="backend/arv_extend_order/controller/arv_order_controller.js"}
// {include file="backend/arv_extend_order/view/list/filter.js"}

Can you help me fix this? I have been trying for ages…

I finally fixed it…
The Problem seems to have been that I tryed to include the files in the app.js and also loaded it via the EventSubscriber