By default the X Theme does not include shortcode support for their topbar display element. In order to add shortcode support, you need to create a child theme, and place this new code in the _topbar.php file. This fix isn’t Memberium specific and will enable all shortcodes for the top bar.
Hat tip to John Cook for the code snippet.
<?php
// =============================================================================
// VIEWS/GLOBAL/_TOPBAR.PHP
// -----------------------------------------------------------------------------
// Includes topbar output.
// =============================================================================
?>
<?php if ( x_get_option( 'x_topbar_display', '' ) == '1' ) : ?>
<div class="x-topbar">
<div class="x-topbar-inner x-container max width">
<?php if ( x_get_option( 'x_topbar_content' ) != '' ) : ?>
<?php $get_topbar_content = x_get_option( 'x_topbar_content' ); ?>
<p class="p-info"><?php echo do_shortcode($get_topbar_content); ?></p>
<?php endif; ?>
<?php x_social_global(); ?>
</div>
</div>
<?php endif; ?>