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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

state = {step: 1};
        render() {
          return <AsyncText ms={100} text={`Step: ${this.state.step}`} />;
        }
      }
      function Spinner() {
        return (
          <Fragment>
            <Text text="Loading (1)" />
            <Text text="Loading (2)" />
            <Text text="Loading (3)" />
          </Fragment>
        );
      }
      const text = React.createRef(null);
      function App() {
        return (
          <Suspense maxDuration={1000} fallback={<Spinner />}>
            <ConcurrentMode>
              <UpdatingText ref={text} />
              <Text text="Sibling" />
            </ConcurrentMode>
          </Suspense>
        );
      }
      
      ReactNoop.renderLegacySyncRoot(<App />);
      await advanceTimers(100);
      expect(ReactNoop.clearYields()).toEqual([