the rewards discount is calculate on product price and not from cart item price. adding this filter the discount is calculate on cart item price

functions.php

<?php

add_filter('ywpar_calculate_product_max_discounts','ywpar_calculate_product_max_discounts', 10, 2);
function ywpar_calculate_product_max_discounts( $price, $product_id ){
	foreach( WC()->cart->get_cart() as $cart_item_key => $values ) {
		$_product = $values['data'];
	
		if( $product_id == $_product->id ) {
			return $_product->get_price();
		}
	}
	return $price;
}