Got the gvr demo code and built it for android. Touch events work perfectly but magnet click doesn't work. Magnet click works for cardboard demo app ( the one that comes bundled with Google cardboard app). So clearly the magnet click works for other apps but doesn't seem to work for the gvr demo.
I even tried triggers for onclick, onpointerdown, onpointerclick. Nothing worked. OnPointerEnter works though. Not sure what's wrong. The cardboard is v1 if that helps.
It was removed when the version v0.9.0 was released (https://developers.google.com/vr/unity/release-notes). In that release we can read:
Magnetic trigger detection has been removed from the SDK, so 2014 Google Cardboard viewers and related models are no longer supported. Please use an older SDK if these viewers are still important to your product.
So the solution I suggest is to use an older version or try to import the code for the magnetic click from that version to the new one.