ReactJS component won't update after first API call

The second parameter of useEffect (the Array) has an important role: the items in that array trigger the useEffect to re-run.

Some cases:

• useEffect(() => {}, []): runs once, after the component is mounted
• useEffect(() => {}, [var1, var2,..., varn]): runs when var1 or var2 or varn is updated
• useEffect(() => {}): runs on every completed re-render (default behavior)

More on useEffect: useEffect hook

So, your code works as expected:

useEffect(() => {
  client.get('items').then((result) => {
    setItems(result.data);
  });
}, []); // -> runs once, when component is mounted

useEffect(() => {
  client.get('items').then((result) => {
    setItems(result.data);
  });
}, [item]); // -> runs when the variable named item changes

you need to organize your code in such a way, that this useEffect hook can run on the update of the variable whose change you want to watch.