Why doesn't coupon discount apply on the products from bundle pack?
Such behavior is expected if the discount amount from a cart price rule is less than the discount provided by a bundle pack. However, if there's a cart price rule that grants a bigger discount compared with a bundle pack discount, the extension can be configured to replace the bundle pack discount with a cart price rule.
To replace the bundle pack item discount with coupons or cart prices rules, please head to Stores → Configuration → Automatic Related Products → Bundle Packs → Replace Bundle Pack Item Discount with Cart Price Rules and set it to Yes.