In the Sandbox environment, I noticed that whenever I would try to change a subscription to another one, not only the PRODUCT_CHANGE event will be triggered on the webhook but also simultaneously an INITIAL_PURCHASE event is also triggered.
I’m testing on a physical android device.

According to this article, it shouldn’t be. In my opinion the more natural way is a PRODUCT_CHANGE followed by a RENEWAL when the new price comes into effect.

Edit: This is a screenshot from the Customer history where the in ‘my opinion’ issue is shown