Spring Data JPA data duplication

I have the following project structure:

public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @OneToMany(mappedBy = "user", fetch = FetchType.EAGER)
    private List<TaskCard> taskCards;
}

public class TaskCard {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @OneToMany(mappedBy = "taskCard", fetch = FetchType.LAZY)
    private List<Task> tasks;

    @ManyToOne(cascade = CascadeType.ALL)
    @JoinColumn(name = "user_id")
    private User user;
}

public class Task {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;  

    @ManyToOne(cascade = CascadeType.ALL)
    @JoinColumn(name = "task_card_id")
    private TaskCard taskCard;
}

And the problem consists here in what. When accessing the POST Task Controller method to create a new task I do the following:

@PostMapping
public Task createTask(@CurrentUser UserPrincipal userPrincipal, @PathVariable("cardId") Long cardId, @RequestBody Task task) {
    User user = userService.findUserById(userPrincipal.getId());
    task.setTaskCard(user.getTaskCards().stream()
                         .filter(card -> card.getId().equals(cardId))
                         .findFirst()
                         .get());
    return taskService.saveTask(task);
}

User Principal is the current user. But it just stores metadata and I take the id from it to find it in the user's database. Here it is worth noting that I am looking for a user in the database and from it I get taskcards and look for the desired card. After that, I assign this value to the new tosk so that it belongs to this card. After that, I save it in the repository. But the problem is that after this, another identical card is created for the User instance, so every time I add a task, I get another copy of the task cards that are in the user. The problem is that I have no idea how they get there or how they are saved. In the database, I have everything in order, the data is not duplicated, but why then when extracting from the database, I do not get the cards that have 'user_id' equal to this user, but everything in a row along with duplicates? It even sounds incomprehensible. I attach screenshots of what my database looks like:

This is users

This is task cards

This is tasks

As you can see in the database everything is in order, there is no duplication, but here's what happens in debug:

I added 5 tasks and in the end I got 5 duplicates of the card, although it should only be one. As you can see, the whole problem is in the "local" user instance, which stores duplicates. How do I fix this?

You are probably join fetching the collections and this is what can happen when you use a List in your model. I suggest you use a Set instead i.e. private Set<Task> tasks;