Sometimes happen blank screen

Sometimes (1-2-3..10 times at day/week) on our site I have blank screen on all pages. And it repair just reloading php-fpm (7.1). In logs I see these

You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'post'  ORDER BY sr_posts.post_date DESC' at line 1 в ответ на запрос SELECT   sr_posts.* FROM sr_posts  WHERE 1=1  AND sr_posts.post_name = '\' AND sr_posts.post_type = 'post'  ORDER BY sr4_posts.post_date DESC , выполненный require('wp-blog-header.php'), wp, WP->main, WP->query_posts, WP_Query->query, WP_Query->get_posts, W3TC\DbCache_Wpdb->query, W3TC\DbCache_WpdbInjection_QueryCaching->query, W3TC\_CallUnderlying->query, W3TC\DbCache_Wpdb->query, W3TC\DbCache_WpdbInjection->query, W3TC\DbCache_Wpdb->default_query

or something similar