I have a class that inherits from SerializedMonoBehaviour. This behaviour has a field (with SerializeField) of a System.Serializable class. This field class has a field (with SerializeField) of an Interface.
SerializedMonoBehaviour - serialized field (serialized class) - serialized field (interface)
The interface field is not serialized, individually or as part of a collection.
The same interface field is serialized when part of the SerializedMonoBehaviour itself.
Changing SerializeField to OdinSerialize does not serialize the field either (reloading the scene clears the references), despite the message about the field not being serialized disappearing.
Unity 2017.4.2f2 Windows 10 x64