The nativized 'Array_Get' custom thunk implementation fails to properly initialize the item returned in the invalid index case.

FCustomThunkTemplates::Array_Get() fails to properly initialize a default item when the index is invalid:

Item = U{};

That will leave the item uninitialized (e.g. UDS types). Should be using the TArray's Inner property to call InitializeValue() instead.

(See UDN thread)

Basically, set up a BP in which you have an array of user-defined struct elements, and then use a 'Get' node to attempt to access an invalid index. The "default" item returned will not be fully initialized in the nativized build.