I am posting here in case you didn't see my reply to the support ticket that you raised.
To help us understand the changes in tracking behaviour that you are seeing would you be able to capture a screen recording of your application being used with our V3 and V5 Developer Preview SDK and share this with email@example.com?
Are you using the tracking module in desktop mode facing up at the bottom of the hands? Any details that you can share on the differences that you are seeing, both good and bad, would be very useful to understand and advise on what is happening here.
if your question is about how you are accessing the hand tracking data please note that from V4.0.0 onwards the legacy APIs were removed in favour of a C style API called LeapC which is closer to the metal. You can find our documentation for this API here.