Hardware Notification We can't find your headset. Please connect your headset.
which is an other annoying problem. But what makes it worse is when the connection to the Rift is back again (triggers HMDAcquired action) the position and the rotation of CenterEyeAnchor is wrong. So when the connection is back, the camera view is not at it's last position but feels like the world has turned and shifted around you.
This problem occurs from Unity 5.6 or higher, but doesn't happen at 5.5.3f1 (all 64bit). Oculus Utilities version doesn't have an effect (tried every version from 1.12 to 1.16 beta).
I was posting this discussion while downloading Unity v2017.1.0f3. I glad to announce that the following configuration solved the problem: Unity v2017.1.0f3, Oculus Utilities v1.16.0, OVRPlugin v1.16.0, SDK v1.16.0.