These are some details from a crash i caught running a dev build:
"[2017.05.27-15.55.49:160][682]LogPhysics:Error: FBodyInstance::GetSimplePhysicalMaterial : GEngine not initialized! Cannot call this during native CDO construction, wrap with if(!HasAnyFlags(RF_ClassDefaultObject)) or move out of constructor, material parameters will not be correct.
[2017.05.27-15.55.49:170][682]LogWindows: Windows GetLastError: The operation completed successfully. (0)
[2017.05.27-15.55.49:412][682]LogWindows:Error: === Critical error: ===
[2017.05.27-15.55.49:412][682]LogWindows:Error:
[2017.05.27-15.55.49:412][682]LogWindows:Error: Assertion failed: GEngine->DefaultPhysMaterial != NULL [File:H:\UnrealEngine-release\Engine\Source\Runtime\Engine\Private\PhysicsEngine\BodyInstance.cpp] [Line: 3583] "