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**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

if (!didResolve) {
        ReactTestRenderer.unstable_yield('Suspend!');
        throw thenable;
      }
      ReactTestRenderer.unstable_yield('Async');
      return 'Async';
    }
    const root = ReactTestRenderer.create(
      <Suspense maxDuration={1000} fallback={<Text text="Loading..." />}>
        <Async />
        <Text text="Sibling" />
      </Suspense>,
      {
        unstable_isConcurrent: true,
      },
    );
    expect(root).toFlushAndYieldThrough(['Suspend!']);
    
    resolveThenable();
    expect(ReactTestRenderer).toHaveYielded([]);
    
    expect(root).toFlushAndYield([
      
      'Async',
      'Sibling',
    ]);
    expect(root).toMatchRenderedOutput('AsyncSibling');
  });
  it('mounts a lazy class component in non-concurrent mode', async () => {
    class Class extends React.Component {