Filter on attributes not filtering?

I’m enjoying the plugin, but it isn’t working as I’d expect, plus I have a couple of questions. I have version 1.3.1.1 installed on my beta site here:

https://beta.dot-art.co.uk/shop/

While the filters on Price and Tags do work as I’d expect, the two based on attributes (Artist and Media) don’t – i.e. when you select an option, all four products remain visible in the right pane. Anything obvious I’m doing wrong here?

A couple of questions:

• I seem to be restricted to four filter options; is this a restriction on the free version, or is there a way to add more?
• Is the major version number (1.3.1.1) indicative of free vs. paid for – i.e. is 2.3.1.1 the equivalent paid version?
• Would the full version allow me to filter on product dimensions?

Thanks.
https://www.ads-software.com/plugins/woocommerce-products-filter/