Reproduction steps:
1) Download and open "915026_repro.zip" project
2) Build and run "scene.unity" scene on an Android device
-- Notice that despite RenderScale is being changed each 2 seconds, screen does not flicker
3) When RenderScale is 0.5 start changing volume using buttons on daydream controller
-- Notice that when RenderScale changes from 0.5 to 1 screen flickers or even goes black

Note:
If we start changing volume when RenderScale is 1 (third point in "Reproduction steps" list) it is very unlikely that we will get this issue reproduced (but once in a while you can observe the issue)

Reproduced with:
5.6.1p1

Tested with
5.6.0f3 and 2017.1.0b7 - both versions have issue reported in case 896321

Devices used for testing:
Google Pixel - Daydream
Samsung Galaxy S6 Edge - GearVR - Does not reproduce