When using this plugin, the maintenance page in its simple version has three issues:

• zooming is blocked through the <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no" /> property : user-scalable-no should be removed, maximum-scale should be either removed or set to 2.0 for example
• no language is set on the page. It should use the site’s language attributes
• the page has no landmark. It can be fixed either by addind a <main> wrapper or adding role="main" to the <div class="wrap">