I'm facing all the issues you mentioned here. Also reported them through the Feedback Assistant. I'm a bit surprised Apple decided to release this API which clearly is not yet ready for third-party developers.

You can take advantage of universal purchases announced in March: Offering Universal Purchase - https://developer.apple.com/support/universal-purchase/. To be able to share auto-renewable subscription products across your apps, they need to use a single bundle ID and be associated with the same app record in App Store Connect. So, if you want to share purchases across your iOS and macOS apps with the same bundle ID, you can do that and the App Store will handle all the logic for you. However, this approach doesn't let you share purchases on a single platform. For example, you have two iOS apps and you want to share purchases between them. Universal purchases can't help you with that. You'll need to build your own back-end solution to keep track of users and their subscription status.

That would be great to provide a description with more context to users. +1 from me.