Can tweet embeds on WordPress be blocked by CSS?



Recently all of our tweet embeds have begun to render as textual blockquotes.

WordPress is able to find the tweet from the URL and the tweet embeds fine in the preview, but the final article looks like this:

Source page:

Are there any obvious steps to troubleshoot this?

The above appears in the <head> of the page:

<script id="twitter-wjs" src="//"></script>

I can’t spot anything obvious and would be grateful for a little input here.