Sorry, this is a duplicate of https://3dclub.orbbec3d.com/t/joints-tracking-problem-when-coming-back-from-out-of-range/1519/3
If i walk backwards away from the camera my body/skeleton stops being tracked. If i walk back up to the camera the skeleton doesn't appear again.
Now I've checked the frame data and it does not report the body as being removed, nor does it report a new body being added.. (I keep a list of body id's to check this fact). in fact the Depth & Color outline renderers etc still show my original outline without disappearing.. it's just the BodyFrame (Skeleton) tracking that does not seem to be correct and fails to update.
I actually have to step out of the camera's view entirely (eg left or right) and step back in, in order to register a new body (which gives a fresh body/skeleton and new Color outline)
This seems like a bug in the SDK rather than a bug in the specific implementation.
(You can test the issue directly in the provided Unity TestScene file)