To reproduce:

1.Download and open attached project.
2.Open "boxWorld" scene.
3.Enter Play mode.

Expected result: Editor not crashing.
Actual result: Editor crashes.

Reproduced with: 5.6.0b10.
Not reproduced with 5.5.1p4, 5.5.0f3.

Notes: Could not test on earlier versions because of compatibility issues. To prevent the crash expand SvrCamera Gameobject, then expand Head GameObject and leave only one active child object by disabling Eye right or Eye left GameObject. If 2 or more child GameObjects of Head GameObject are active editor experiences a crash. The scripts which likely cause the crash are created on these active child objects when Play Mode is active.