IL2CPP fails to handle data in a struct when the following conditions are met:

- This struct implements an interface.
- This struct is given to a generic class as a type parameter.
- This type parameter is constrained with the interface.

See the following pseudocode. In this case, Handler<Data> causes a problem.

interface IData { .. }

struct Data : IData { .. }

class Handler<T> where T : struct, IData { .. }