Defer attribute on scripts being removed?

Run in to a problem with the “defer” attribute being removed from my scripts on one of my websites.

When W3TC is disabled, both scripts have the defer attribute:

<script type="text/javascript" src="https://www.google.com/recaptcha/api.js?render=X&amp;ver=2.0.2" id="gforms_recaptcha_recaptcha-js" defer="defer" data-wp-strategy="defer"></script>

<script type="text/javascript" src="https://example.com/app/plugins/gravityformsrecaptcha/js/frontend.min.js?x39172&amp;ver=2.0.2" id="gforms_recaptcha_frontend-js" defer="defer" data-wp-strategy="defer"></script>

When W3TC is enabled, the minified version has the attribute removed:

<script type="text/javascript" src="https://www.google.com/recaptcha/api.js?render=X&amp;ver=2.0.2" id="gforms_recaptcha_recaptcha-js" defer="defer" data-wp-strategy="defer"></script>

<script  src="https://example.com/app/cache/minify/e2eea.js?x39172"></script>

This causes a problem, since the e2eea script requires the reCAPTCHA library.

Curiously, on one of my other websites this is not happening:

When W3TC is enabled, the minified version has a single “defer” attribute (preserved):

<script src="https://www.google.com/recaptcha/api.js?render=X&amp;ver=2.0.2" id="gforms_recaptcha_recaptcha-js" defer data-wp-strategy="defer"></script>

<script  defer src="https://example.co.uk/app/cache/minify/e2eea.js?x14114"></script>

As far as I can tell, the W3TC configurations are pretty much the same for both websites:

diff broken working
67c67
<     "lazyload.enabled": true,
---
>     "lazyload.enabled": false,
1078,1080c1078,1080
<     "page": "w3tc_minify",
<     "_wpnonce": "e692661fe3",
<     "_wp_http_referer": "\/wp\/wp-admin\/admin.php?page=w3tc_minify&w3tc_message=68ee51307695c&w3tc_note=flush_all",
---
>     "page": "w3tc_general",
>     "_wpnonce": "beaaf92399",
>     "_wp_http_referer": "\/wp\/wp-admin\/admin.php?page=w3tc_general",
1131,1134c1131,1132
<     "allcache.wp_cron": "0",
<     "pgcache.wp_cron": "0",
<     "minify.wp_cron": "0"
< }
---
>     "allcache.wp_cron": "0"
> }
\ No newline at end of file

Both websites are running W3TC 2.8.13, Gravity Forms reCAPTCHA 2.0.2. The working website is an Elementor website, the other a WPBakery website, but I cannot fathom why one is getting the defer script stripped out?