This issue has been marked as Won't Fix due to priority. As a workaround, please use the screenshot functionality on the GearVR itself.
Using the shot console command or the RequestScreenshot function to take a screenshot in Gear VR causes the app to crash. This was tested on Android-19, ETC-1 configuration, with both Developer Mode Gear VR and the actual Gear VR headset.
This also occurs in 4.15
Unable to test this in Main as I am being blocked by not being able to even launch a Gear VR app on Android.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-47195 in the post.