useState() hook removes fields from the object when setting new value

Can't understand what I'm doing wrong here. I have a very simple object state:

const [itemInput, setItemInput] = useState({
    userId: userId,
    objectId: id,
    title: "",
    description: "",
    createdAt: new Date().getTime().toString(),
  })

Then, I have an input that changes the title field:

const onChange = (e) => {
    setItemInput((prevState) => ({
      ...prevState,
      [e.target.name]: e.target.value,
    }));
  };

And this is how onChange is used:

<input
        type="text"
        className="item-description-input"
        placeholder="Add description..."
        name="title"
        value={itemInput.title}
        onChange={onChange}
      />

GraphQL endpoint:

export const CREATE_ITEM = gql`
  mutation createItem($itemInput: ItemInput!) {
    createItem(itemInput: $itemInput) {
      userId
      objectId
      title
      description
      createdAt
    }
  }
`;

Submit function:

const onAddItemClick = (e) => {
    e.preventDefault();
    createItem({
      variables: {
        itemInput: itemInput,
      },
    }).then((res) => {
      console.log(res);
    });
  };

When submitting, I get:

message: "Variable "$itemInput" got invalid value { title: "ddd" }; Field "userId" of required type "MongoId!" was not provided." 

And this error is repeated for all the remaining fields but title.

If I console.log(itemInput) when the functional component is loaded, I get the initial state of the object. However if I add console.log(itemInput) after onChange, I get only {title: "some_added_text"}. onChange removes the other fields from the object, and, on submit, my graphQL endpoint returns an error that the other fields are not provided. This is very frustrating, as I seem to be doing everything correctly.

UPD: Added the components. Object component gets the list of objects. Each Object has Items. The problematic code is in the Items component when I want to add a new Item to that Object.

Object (parent) component:

import React, { useState, useReactiveVar, Fragment } from "react";
import { useMutation } from "@apollo/client";
import CREATE_OBJECT from "../../mutations/Object";
import { objectsVar } from "../../cache";

//Components
import ItemContainer from "./ItemContainer";

const Container = ({ data, userId, color }) => {
  const [objectInput, setobjectInput] = useState({
    title: "",
    userId: userId,
    createdAt: new Date().getTime().toString(),
    color: color,
  });

  const [createObject] = useMutation(CREATE_OBJECT);

  const onAddClick = (e) => {
    e.preventDefault();
    createObject({
      variables: {
        objectInput: objectInput,
      },
    }).then((res) => {
      setobjectInput({
        title: "",
        userId: userId,
        createdAt: new Date().getTime().toString(),
        color: color,
      });
    });
  };
  
  // This works perfectly fine!! 
  const onChange = (e) => {
    setobjectInput({ ...objectInput, [e.target.name]: e.target.value });
  };

  objectsVar(data);
  const objects = useReactiveVar(objectsVar);

  return (
    <div>
      <div>
        <input
          type="text"
          placeholder="Add description..."
          name="title"
          value={objectInput.title}
          onChange={onChange}
        />
      </div>
      <div onClick={onAddClick}>Add object</div>
      {objects && objects.getAllObjects.length === 0 ? (
        <p>No objects</p>
      ) : (
        <Fragment>
          {objects &&
            objects.getAllActiveSwimlines.map(({ _id, title, items }) => (
              <ItemContainer key={_id} id={_id} title={title} userId={userId} items={items} />
            ))}
        </Fragment>
      )}
    </div>
  );
};

export default Container;

Item (child) component:

import React, { useState, Fragment } from "react";
import ItemContainer from "../Item/ItemContainer";
import { useMutation } from "@apollo/client";
import { CREATE_ITEM } from "../../mutations/Item";

const ItemContainer = ({ id, title, items, userId }) => {
  const [itemInput, setItemInput] = useState({
    userId: userId,
    objectId: id,
    title: "initial state",
    description: "test desc",
    createdAt: new Date().getTime().toString(),
  });

  // This doesn't work!
  const onChange = (e) => {
    const { name, value } = e.target;
    setItemInput({
      ...itemInput,
      [name]: value,
    });
  };

  const [createItem] = useMutation(CREATE_ITEM);

  const onAddItemClick = (e) => {
    e.preventDefault();
    createItem({
      variables: {
        itemInput: itemInput,
      },
    }).then((res) => {
      setItemInput({
        userId: userId,
        objectId: id,
        title: "",
        description: "",
        createdAt: new Date().getTime().toString(),
      });

      console.log(res);
    });
  };

  const newItemInput = (
    <div>
      <input
        type="text"
        placeholder="Add description..."
        name="title"
        value={itemInput.title}
        onChange={onChange}
      />
      <div onClick={onAddItemClick}>Add item</div>
    </div>
  );

  const itemContent = (
    <div>
      <Fragment>
        {items &&
          items.getObjectItems.map(({ _id, title }) => (
            <Item key={_id} id={_id} title={title} />
          ))}
      </Fragment>
    </div>
  );

  return (
    <div>
      {newItemInput}
      {itemContent}
    </div>
  );
};

export default ItemContainer;

What am I missing here?