Timeout error

The way to find out where it times out is to add exit() clauses to the relevanssi_highlight_terms() function in /lib/excerpts-highlights.php to see how far it gets before it times out. Other than that, it’s hard to say. When Relevanssi adds the highlights, it makes a bunch of regex queries on the page; that shouldn’t be terribly hard, but if the page is long enough, I guess it can get complex.

You can disable the highlighting on that specific page by adding a filter hook on relevanssi_highlight_docs option to turn it to off for that page:

add_filter( 'pre_option_relevanssi_highlight_docs', function( $value ) {
  global $post;
  if ( 3587 === intval( $post->ID ) ) {
    return 'off';
  }
  return $value;
} );