The log from Xcode tells, that crash connected with this error:
ShippingLog: [186] Jul 6 10:18:55 iPhone-Daniil SpringBoard(KeyboardArbiter)[212] : HW kbd: Failed to set (null) as keyboard focus
And it appears only with Shipping build and GoogleVR plugin enabled.
And I fully support hirapong: UE-41244 seems to be a different to this issue, especialy, UE-41244 - seems to be solved, because there is no crash with Switch button in UE 4.16.2