When WordPress upgrades plugins and themes, it will enable maintenance mode to prevent website modifications during the update. But, in some cases, this maintenance mode will not get disabled after the upgrade, and your website will be inaccessible. What can you do?
WP activates maintenance mode when upgrading the active plugin, or when in network/multisite environment. In same very rare cases, this mode doesn’t get disabled after the upgrade. But, you can disable it using FTP. Simply, open FTP and connect to your website, in the website root directory where wp-config.php, wp-load.php, wp-login.php and wp-admin are, you will see file called: ‘.maintenance‘. Yes, it starts with the dot, just like .htaccess does. Simply delete that ‘.maintenance‘ file and your website will start working again.
Good thing is that even if you don’t remove this file, it can be active only for 10 minutes. If that file is older than 10 minutes, WordPress will ignore it and resume normal work.
If you don’t have FTP access to your website, you can use access through your hosting control panel or you need to contact your hosting company and get their support people to remove that file for you.