I figured this issue out myself, but thought I’d post the problem here anyway. After installing SlimSEO the website had NO TITLES! Not a great start for a SEO plugin that purports to be easy to use. I’ve used many other SEO plugins and they work with my custom built themes straight out of the box. For this website, SEO is low priority so I thought I’d try a ‘simpler’ SEO plugin just to provide ability to edit titles and descriptions. In my theme’s header I have a title tag:
<title><?php wp_title(); ?></title>
This is a standard setup for many themes. I figured out that to get SlimSEO to work, I had to add add_theme_support( ‘title-tag’ ) to functions.php and remove the title tag! I’m curious, why make users through these hoops and why is it not clearly documented?