Problem Description
When loading the Yoast SEO plugin, you get a blank screen wherein you only see the WordPress admin menu and title bar, but there's nothing where the Yoast settings typically appear.Problem Resolution
This issue is caused by a missing dependency. Yoast SEO now requires the php-bcmath library.If you're on a shared server, you'll probably need to ask your hosting provider to install the missing library. If you're on your own virtual server or a dedicated machine you can fix the issue by installing the php-bcmath library. For example on CentOS servers you would run:
yum install php-bcmath
On Plesk servers, if you're using a secondary installed version of PHP installed through Plesk, it should auto-install bcmath for you. If not, then you can always run:
yum install plesk-php56-bcmath
or yum install plesk-php70-bcmath
Simply replace the PHP version that you have active for the domain.