Fast Velocity Minify
The Fast Velocity Minify plugin has a setting under “HTML Options” to strip HTML comments:
This setting also strips HTML comments from listing pages. On all types of listing templates (except ones that use a FacetWP shortcode template) this will cause problems, because FacetWP needs the <!--fwp-loop--> HTML comment to automatically add a facetwp-template class on the element surrounding the results. This class is needed to dynamically replace the HTML within this element when filtering. Without this class, FacetWP does not know which content to dynamically replace.
Turning off HTML minification fixes this problem. However, if you want to keep HTML minification, you also can also add the facetwp-template class to your templates manually. Simply add the class to the parent element of your post loop. On WooCommerce shop pages, you can use these hooks that do the same.