You can add Wordfence to this list of plugins which Plugins Garbage Collector can't clean out. I used Wordfence on all of my WP sites up until about six months ago when it started to conflict with another plugin I needed, so I deleted Wordfence from all of my sites.
When I run your plugin, I find well over a dozen tables, all with the prefix wp-wfxxxxxx and some of them have thousands of entries and take up 2-3mb! But when I select them all and hit 'Delete Tables', I get the following error message "Unknown table 'luxurywa_wp1.wp_wfbadleechers' " which is the first of the tables on the list. If I re-run 'Search None-WP Tables' (that should be Non-WP, not None-WP by the way), all the wp_wfxxxxx tables are back again, so the plugin isn't doing anything to them.
I have tried both v0.9.14 and the latest v0.9.15 with no difference. If you need any further information, let me know, I would be happy to help because this is a plugin that is badly needed!