What are you storing in the TDoubleLinkedList, and what is the linked list held inside? As a normal member (not a UPROPERTY) the list and its contents will be cleaned up when the owner is destructed, the issue is the garbage collector can’t know the list or its contents exist for reference-counting purposes - this matters if you’re storing UObject pointers, directly or indirectly (inside stored structs). You also need to be aware that the linked list won’t be able to be “saved” automatically, since Unreal’s default serialization works through UProperties.