<!--
  Note: if the issue is about documentation or the website, please file it at:
  https://github.com/reactjs/reactjs.org/issues/new
-->

**Do you want to request a *feature* or report a *bug*?**
bug, I believe, unless I misunderstand how it works
**What is the current behavior?**
Given a `Suspense` inside `Suspense` case like
```
<Suspense fallback="Fallback 1">
  <LazyText1 text="First text" />
  <Suspense fallback="Fallback 2">
    <LazyText2 text="Second text!" />
  </Suspense>
</Suspense>
```

Promises in `LazyTexts` start resolving at the same time, but if `LazyText2` is resolved first it never renders, `Fallback 2` stays.

Result:
```
First text

Fallback 2
```

Please see https://codesandbox.io/s/234o4zry7n

**What is the expected behavior?**

Every `LazyText` displayed in the end
```
First text

Second text!
```

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**
react, react-dom 16.6.0

componentDidMount() {
        ReactTestRenderer.unstable_yield('Did mount: ' + this.props.label);
      }
      componentDidUpdate() {
        ReactTestRenderer.unstable_yield('Did update: ' + this.props.label);
      }
      render() {
        return <Text text={this.props.label} />;
      }
    }
    async function fakeImport(result) {
      return {default: result};
    }
    const LazyClass = React.lazy(() => fakeImport(Class));
    const root = ReactTestRenderer.create(
      <Suspense fallback={<Text text="Loading..." />}>
        <LazyClass label="Hi" />
      </Suspense>,
    );