Why did the metrics drop after site optimization?

Question

Yandex.Metrica

Hello, friends!
On the site (both in the old code and in the new one), at the bottom, in the footer, there are Metrica and LiveInternet counters.
The new code was launched on the site just before the New Year 2019.
As a result, the download speed increased, the Google Speed ​​test showed excellent optimization results. Outwardly, on all browsers and gadgets, everything also looks and works perfectly. But, oddly enough, Yandex.Metrica immediately showed a deterioration in two indicators of the site:
1. Attendance by Metrica sank relative to LiveInternet by 50-100 people per day. Previously, Metrica always showed attendance more than Li by about the same 50-100 people per day. And given that Metrica "sees" even those visitors that Li "does not see" (for example, those who have disabled JS), then Metrica should show more
2. "Bounces" have increased. With the old code, failures were at the level of 7-8%, with the new code, failures steadily became 9.5-10.5%.
What could be the reason for such "miracles"?
What was done:
1- Removed all (except SEO and CKeditor) plugins and added the necessary functions.
2- Only the code (HTML, CSS, JS) for this page was left on the page, nothing extra on the pages is loaded, no hidden elements.
3- Disabled some WordPress functionality:

// Отключаем сам REST API
  add_filter('rest_enabled', '__return_false');
  
  // Отключаем фильтры REST API
  remove_action( 'xmlrpc_rsd_apis',            'rest_output_rsd' );
  remove_action( 'wp_head',                    'rest_output_link_wp_head', 10, 0 );
  remove_action( 'template_redirect',          'rest_output_link_header', 11, 0 );
  remove_action( 'auth_cookie_malformed',      'rest_cookie_collect_status' );
  remove_action( 'auth_cookie_expired',        'rest_cookie_collect_status' );
  remove_action( 'auth_cookie_bad_username',   'rest_cookie_collect_status' );
  remove_action( 'auth_cookie_bad_hash',       'rest_cookie_collect_status' );
  remove_action( 'auth_cookie_valid',          'rest_cookie_collect_status' );
  remove_filter( 'rest_authentication_errors', 'rest_cookie_check_errors', 100 );
  
  // Отключаем события REST API
  remove_action( 'init',          'rest_api_init' );
  remove_action( 'rest_api_init', 'rest_api_default_filters', 10, 1 );
  remove_action( 'parse_request', 'rest_api_loaded' );
  
  // Embeds связанные с REST API
  remove_action( 'rest_api_init',          'wp_oembed_register_route'              );
  remove_filter( 'rest_pre_serve_request', '_oembed_rest_pre_serve_request', 10, 4 );
  
  remove_action( 'wp_head', 'wp_oembed_add_discovery_links' );
  // вставки из других сайтов
  remove_action( 'wp_head', 'wp_oembed_add_host_js' );
  
  add_filter('xmlrpc_enabled', '__return_false');

Answer 1

This question will be answered by your own metric. Stop looking at the visitors - look at the pages in the index queries and everything else. Maybe you cut something that affected the indexing or something. Without a detailed debriefing blindly, here you can only guess on the coffee grounds

Answer 2

What is the relationship between optimization and attendance?
Or by optimization you mean changing:
- design
- functionality
- content
- html structure
If it hasn't been changed, then there is no correlation with optimization.