Sandbox: https://codesandbox.io/s/cranky-kapitsa-op3jh

Repro: type "a" and then after a second "b"

Expected: Eventually you'll see "ab" in all fields. Pending "..." indicator goes away.

Actual: You'll keep seeing "a" in low pri field. Pending "..." indicator is stuck.
const [step, setStep] = useState(0);
      const [shadow, _dispatch] = useReducer(() => step, step);
      dispatch = _dispatch;
      if (step < 5) {
        setStep(step + 1);
      }
      Scheduler.unstable_yieldValue(`Step: ${step}, Shadow: ${shadow}`);
      return shadow;
    }
    ReactNoop.render(<App />);
    expect(Scheduler).toFlushAndYield([
      'Step: 0, Shadow: 0',
      'Step: 1, Shadow: 0',
      'Step: 2, Shadow: 0',
      'Step: 3, Shadow: 0',
      'Step: 4, Shadow: 0',
      'Step: 5, Shadow: 0',
    ]);
    expect(ReactNoop).toMatchRenderedOutput('0');
    act(() => dispatch());
    expect(Scheduler).toHaveYielded(['Step: 5, Shadow: 5']);
    expect(ReactNoop).toMatchRenderedOutput('5');
  });
  it('should process the rest pending updates after a render phase update', () => {
    
    
    let updateA;
    let updateC;
    function App() {