Paul Jorgensen ジョルゲンセン ポール

Thanks to all for pointing out the error on the site. It’s an open bug on GitHub for Automattic’s JetPack.
Here’s the fix from the bug thread:

The following change to the core function get_the_content() eliminates the problem

if ( is_array( $pages ) ) {
    if ( $page > count( $pages ) ) // if the requested page doesn't exist
        $page = count( $pages ); // give them the highest numbered page that DOES exist
} else {
    $page = 0;
}

… which I did from my Nexus 6P via ssh in a Termux session!