I was able to resolve this issue after speaking with Relevanssi support. My final _content-post-header.php
child file looks like this:
<?php
// =============================================================================
// VIEWS/INTEGRITY/_CONTENT-POST-HEADER.PHP
// -----------------------------------------------------------------------------
// Standard <header> output for various posts.
// =============================================================================
?>
<header class="entry-header">
<?php if ( is_single() ) : ?>
<h1 class="entry-title"><?php the_title(); ?></h1>
<?php elseif ( is_search() && function_exists( 'relevanssi_the_title' ) ) : ?>
<h2 class="entry-title">
<a href="<?php the_permalink(); ?>" title="<?php echo esc_attr( sprintf( __( 'Permalink to: "%s"', '__x__' ), the_title_attribute( 'echo=0' ) ) ); ?>"><?php relevanssi_the_title(); ?></a>
</h2>
<?php else : ?>
<h2 class="entry-title">
<a href="<?php the_permalink(); ?>" title="<?php echo esc_attr( sprintf( __( 'Permalink to: "%s"', '__x__' ), the_title_attribute( 'echo=0' ) ) ); ?>"><?php x_the_alternate_title(); ?></a>
</h2>
<?php endif; ?>
<?php x_integrity_entry_meta(); ?>
</header>
Also to clarify the previous message from @paul.r - since i’m using Pro and not X, this path is not accurate:
wp-content/themes/x-child/framework/views/{your-stack}/
My child file needed to go here:
wp-content/themes/pro-child/framework/views/{your-stack}/