could you please try with a default theme (twenty something, storefront) if the problem persists? Is the coupon itself being applied?
In version 2.3.3 of the plugin, which is about to be released soon, I added two filters you can use to change the amount of free products / bogo products to be added. The filters are:
wjecf_bogo_product_amount_for_coupon( $quantity, $coupon ) // for BOGO products wjecf_free_product_amount_for_coupon( $quantity, $coupon ) // for FREE products
You can apply any logic to change the amount of free products to be added using these filters.
You can use API function
WJECF_API()->get_quantity_of_matching_products( $coupon ) to retrieve the amount of matching products in the cart.
You can download 2.3.3-b5 (see your account page) to have this functionality already.