No two products in a subscription group can be active at the same time.
iOS Subscription Groups Explained
Jacob Eiting

Hi Jacob, love what you guys are building. Need help clarifying something, in your ‘manage subscriptions’ screenshot you have 2 products active at the same time, is this because ‘Meal Manager — Breakfast’ is in another subscription group and therefore can be active alongside ‘Meal Manager-Dinner’? So a user can have two subscriptions active in the same app but they need to be in different subscription groups? Hope that makes sense!