Creating a new BB custom module which references other plugins' shortcodes (not working)

There are a few posts similar to this one, but not exact. I am trying to create a custom module for BB which I can use on other pages and posts – it’s really just aggregating a bunch of functionality. The shortcode always renders as a string literal and never as the content emitted by the shortcode’s associated plugin. Here is some sample code:

<?php if($settings->show_read_time == "option-yes"){ ?>
<div class="iss-post-metadata1-container">
	<span class="iss-post-metadata1-label">Reading Time:</span><br/>
	<?php echo do_shortcode('[rt_reading_time postfix="minutes" postfix_singular="minute"]', false); ?>
</div>
<?php } ?>

The resulting page/post will have the literal string outputted:
[rt_reading_time postfix=“minutes” postfix_singular=“minute”]

It should show something like:
3 minutes

When I look at the global $shortcode_tags, I don’t see the plugins I am after, although I know they exist because I can use them outside of this BB module.

Insights appreciated.