The plugin doesn't generate thumbnails for the Woocommerce thumbnail's size

you should also install simple images – this will let you manage all image sizes under media settings – including the woocommerce image sizes.

From there, it might be more clear what image sizes are available.

your gallery thumb is the tiny thumbs on the product page for the gallery images
the category thumb is the larger thumb that displays in the category/shop view and the shop single is the main image on the product page.