To fix it, I changed line 3405 in rsvpmaker-pluggable.php from
wp_enqueue_script(‘rsvpmaker_js’,plugins_url(‘rsvpmaker/rsvpmaker.js’), array(), filemtime( plugin_dir_path( __DIR__ ) . ‘rsvpmaker.js’ ));
to:
wp_enqueue_script(‘rsvpmaker_js’,plugins_url(‘rsvpmaker/rsvpmaker.js’), array(), filemtime( plugin_dir_path( __DIR__ ) . ‘rsvpmaker/rsvpmaker.js’ ));
hopefully there will be no adverse effects..