iframes at top of the page are not loaded

[wesleybl]

We have a site with iframes at the top and they sometimes don't load. I believe this is because of the use of async here:

collective.lazysizes/webpack/app/resources.pt

Line 2 in da01ba8

<script async tal:attributes="src <%= 'string:${view/site_url}/' + htmlWebpackPlugin.files.js[js] %>"></script>

When the script is executed, the HTML parse has not finished and therefore the iframe is not loaded. Since the iframe is already on the screen, there is no scroll event to "load the iframe"

When I change to defer, it worked. Would it be interesting to change it to defer?