The Get HMD worn State does not update the worn state when the headset is put on/taken off. Rather it only updates when the headset sleeps or wakes ups. This means that the headset can be taken off/put on without ever updating the worn state.
Results: The Heads set only updates when it activates (not when put on or taken off)
Expected: The head set would update the worn state when the headset it put on and when it was taken off
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-67103 in the post.