Temporaru fix for -- https://github.com/bu-ist/bu-versions/issues/19

functions.php

add_action('template_redirect', function() {
	if( get_query_var('version_id') )
  	preview();
});

function preview() {

	global $post;
	
	if ( ! is_object($post) )
			return $post;

		$version_id = (int) get_query_var('version_id');
		$preview = wp_get_post_autosave($version_id);
		if ( ! is_object($preview) ) {
			$preview = get_post($version_id);
			if( !is_object($preview)) return $post;
		}

		$preview = sanitize_post($preview);

		$post->post_content = $preview->post_content;
		$post->post_title = $preview->post_title;
		$post->post_excerpt = $preview->post_excerpt;

		// Workaround for `redirect_canonical` logic added in 4.0
		// See https://core.trac.wordpress.org/changeset/28874
		if ( 'page' === get_option( 'show_on_front' ) && $post->ID == get_option( 'page_on_front' ) ) {
			add_filter( 'redirect_canonical', '__return_false' );
		}
	
}