php - Why did crash our WordPress site?

one text

There is no doubt, our WordPress site is heavy loaded, but why it crashed, and why we couldn't restart it on Cloudways only rollback it?

I see hungreds of similar lines before the crash like:

[Tue Apr 13 15:12:25.882171 2021] [proxy_fcgi:error] [pid 6670:tid 139911898322688] [client 89.135.146.241:13425] AH01079: failed to make connection to backend: httpd-UDS, referer: https://www.palferi.hu/hanganyagok/2006-2007/2007-01-02/

And after the crash, 4 similar line like:

[Wed Apr 14 10:34:50.809931 2021] [proxy_fcgi:error] [pid 1200:tid 140238550603520] [client 138.197.189.13:52981] AH01071: Got error 'PHP message: WordPress adatb\xc3\xa1zis hiba Table 'hudxsgwarf.wpar_posts' doesn't exist a lek\xc3\xa9rdez\xc3\xa9sben SELECT wpar_posts.* FROM wpar_posts LEFT JOIN wpar_term_relationships ON (wpar_posts.ID = wpar_term_relationships.object_id) WHERE 1=1 AND ( \n wpar_term_relationships.term_taxonomy_id IN (1,86)\n) AND wpar_posts.post_type IN ('post', 'hanganyagok', 'csoportok', 'programok', 'teljess-gre-hangolva') AND (wpar_posts.post_status = 'publish') GROUP BY wpar_posts.ID ORDER BY wpar_posts.post_date DESC k\xc3\xa9sz\xc3\xadtette require('wp-blog-header.php'), wp, WP->main, WP->query_posts, WP_Query->query, WP_Query->get_posts, do_action_ref_array, WP_Hook->do_action, WP_Hook->apply_filters, WPSEO_Sitemaps->redirect, WPSEO_Sitemaps->get_sitemap_from_cache, WPSEO_Sitemaps->refresh_sitemap_cache, WPSEO_Sitemaps->build_sitemap, WPSEO_Sitemaps->build_root_map, WPSEO_Taxonomy_Sitemap_Provider->get_index_links, WP_Query->__construct, WP_Query->query, WP_Query->get_posts\n', referer: https://www.palferi.hu/sitemap_index.xml

Do you have any idea what were happen? Cloudways claim, CPU power was short to serve the requests. I do not know.