Multiple active subscriptions within the same subscription group

We have 2 monthly subscription tiers that are part of a subscription group, and always have been part of this group. Both are configured with a 1 month trial introductory offer. According to the documentation for auto-renewable subscriptions,:

Users can subscribe to one subscription product per group at a time.

And yet several users have managed to start trials of both products in this group simultaneously, which converted to paid subscriptions after the expiration of the trials, and now are being concurrently billed by Apple for both. How do we completely prevent this from happening?

Did you develop your subscriptions purchase process using Apple's "SubscriptionStoreView" or have you developed your own subscription purchase view? I am currently testing my subscriptions purchase process using TestFlight and sandbox accounts ... I have developed my subscriptions purchase process using the "SubscriptionStoreView" ... I have never seen this multiple subscription purchases when testing using Xcode & Simulator and Xcode & iPhone ... Conceptually, I believe it should not matter whether you developed your own view or not, Store Kit 2 should properly handle subscription purchases properly and prevent duplicated subscriptions because a new subscription should only become active when the previous subscription is expires or is upgraded.

Multiple active subscriptions within the same subscription group
 
 
Q