In a Gear VR player using Single-Pass Stereo built with Unity 2017.2.0b11, if the Render Viewport Scale is changed via script then there will be after-images of the scene geometry because the background does not clear consistently, plus altogether extraneous copies of the scene geometry will appear.

I saw this problem occur on S7 Gear VR with Mali chips.

This problem does not occur on Gear VR using multi-pass stereo.

This problem does not occur on Vive in Play mode using multi-pass, single-pass, or stereo instancing.

This problem does not occur on Mock HMD in Play mode using multi-pass, single-pass, or stereo instancing.

This problem does not occur on Gear VR using a SPS mode player built with Unity 2017.2.0b10.