Large amount of errors started to appears

As of yesterday, my error log started to file up with errors like
mysql_get_server_info() expects parameter 1 to be resource, boolean given in /public_html/wp-content/db.php on line 318

Nothing's changed on my server in regards to the database in several days. But I have noticed over the past 24 hours that the site has issues connecting to the database (indicated by WordPress database connection error when accessing the dashboard) and the website not being resolved and showing a plain white page (several refreshes later and it's back).

FWIW, I also see this related MySQL error WordPress database error MySQL server has gone away for query SELECT option_value FROM wp_9_options WHERE option_name = 'img_width' LIMIT 1 made by require('wp-blog-header.php'), require_once('wp-load.php'), require_once('wp-config.php'), require_once('wp-settings.php'), include_once('/plugins/nwcup-featured-content-slider/featured-content-slider.php'), get_option, m_wpdb->query

WordPress database error for query SELECT meta_value FROM nwtd_prosites_global.wp_sitemeta WHERE meta_key = 'ultimatebranding_activated_modules' AND site_id = 1 made by require('wp-blog-header.php'), require_once('wp-load.php'), require_once('wp-config.php'), require_once('wp-settings.php'), do_action('plugins_loaded'), call_user_func_array, UltimateBrandingPublic->load_modules, ub_is_active_module, get_ub_activated_modules, ub_get_option, get_site_option, m_wpdb->query

Any clue what could be going on?