SiteStatsUpdate has code to try to stop stats from going negative, however it doesn't work.
Updating site stats...Wikimedia\Rdbms\DBQueryError from line 1230 of /vagrant/mediawiki/includes/libs/rdbms/database/Database.php: Error 1690: BIGINT UNSIGNED value is out of range in '`wiki`.`site_stats`.`ss_good_articles` - 1' Function: MediaWiki\Deferred\SiteStatsUpdate::doUpdate Query: UPDATE `site_stats` SET ss_total_edits = GREATEST(`ss_total_edits`-1,0),ss_total_pages = GREATEST(`ss_total_pages`-1,0),ss_good_articles = GREATEST(`ss_good_articles`-1,0) WHERE ss_row_id = 1