Meta tag getting stripped off in AMP List/Mustache

Question

I am trying to add ItemList MicroData for Schema but the Meta tag is getting stripped off in the amp-list/mustache. Here's the code I am using for Microdata:

<div itemscope itemtype="https://schema.org/ItemList">
    <span itemprop="name"><?php $title; ?></span>
    <link itemprop="itemListOrder" href="https://schema.org/ItemListOrderDescending" />
    <amp-list height="100" width="auto" load-more="auto" src="https://www.flixwatch.co/stagin/list-schema/?post_id=<?php echo $post->ID; ?>" binding="no">
       <template type="amp-mustache">
        <div itemprop="itemListElement" itemscope itemtype="https://schema.org/ListItem">
            <meta itemprop="position" content="{{rank}}"/>
            <div itemprop="url">{{url}}</div>
        </div>
       </template> 
    </amp-list>
</div>

But in the output, the meta tag is getting stripped.

Here's an example, how it should look.

I have tried adding the {{position}} in Div instead of meta tag but it's not valid as per the rich results test either. Any idea, how to get it working?