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If you can not see .maintenance file in your site’s root directory, then make sure you checked your FTP client to show hidden files. In Filezilla, you can force it to show hidden files by clicking on Server ? Force showing hidden files from the menu bar.

WordPress creates a .maintenance file during the update process which indicates that your site is in the maintenance mode. Unless this file is removed your site will remain in the maintenance mode and your users will continue to see the notification.

I had this issue and I couldn’t find the .maintenance file (I thought my boss was going to kill me lol) so what I did was rename the plugin folder that was causing the issue. It allowed me to get into our site’s backend and once there, I went back into cpanel’s file manager and changed the plugin’s folder name back to its original name and updated the plugin through wordpress. I can confirm that this has worked for Emfurn.com