The version currently installed is 2.3.2. Earlier, we updated (via the WP admin) to version 2.4.4. When we did, it caused all sites in our multisite network to go down. All sites responded with an Internal Server Error.
In our logs, this is the error we came across:
PHP Fatal error: require_once(): Failed opening required '<path-to-site>/wp-content/plugins/ad-inserter/includes/dst/dst.php' in <path-to-site>/wp-content/plugins/ad-inserter/ad-inserter.php on line 7168
Some extra info:
WordPress version: 4.9.9
PHP version: 5.6