I have been facing this same issue all night long. As far as I can guess, it is an issue on Apple's side. It is very frustrating.

I am looking for the same answer. If AppleID A creates a subscription with User 1, I want User 1's UUID attached to the subscription through the appAccountToken. If User 1 cancels subscription, then AppleID A subscribes again with User 2, I want to attach User 2's UUID to the subscription via appAccountToken. Currently, I am seeing that User 1's appAccountToken stays with the subscription when User 2 starts a subscription.

After a month of fighting this issue, I finally realized there is an option in Xcode to adjust the renewal rate (it doesn't matter what the Sandbox tester renewal rate is). Steps: Select StoreKit Configuration File. Select Editor from menu. Select Subscription Renewal Rate. Choose a renewal rate.