Original refresh token never expires, agreed. But it can be invalidated by making changes to user profile. After such user actions, Apple will return invalid_grant. So far so good. But why is there a throttle limit of one request per day. Moreover access token issued by Apple expires in 3600 seconds.

The access token issued by Apple will expire in 3600 seconds. The only way to get a new token is redeeming it via refresh token. Then why is there a rule to throttle such calls if requested more than once a day. Absurd!