The standard behavior when the player holds down the reset controller button on the GearVR controller is:
1/ The GearVR controller’s orientation is reset
2/ The orientation of the camera remains unchanged.
This has been the standard behavior in all version of the UE4, up to the version 4.21.
In version 4.21, when the player holds down the reset controller button on the GearVR controller, this happens:
1/ The GearVR controller’s orientation is reset
2/ the orientation of the camera is also reset to face the world X axis. (the camera Yaw is reset to 0.0)
This is an engine function which cannot be modified or fixed and there is noway to get a notification when the player holds down this button.