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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

// 
          // 
          break;
        }
        previousScheduledRoot = root;
        root = root.nextScheduledRoot;
      }
    }
  }
  nextFlushedRoot = highestPriorityRoot;
  nextFlushedExpirationTime = highestPriorityWork;
}
// TODO: This wrapper exists because many of the older tests (the ones that use
// flushDeferredPri) rely on the number of times `shouldYield` is called. We
// should get rid of it.
let didYield: boolean = false;
function shouldYieldToRenderer() {
  if (didYield) {
    return true;
  }
  if (shouldYield()) {
    didYield = true;
    return true;
  }
  return false;
}
function performAsyncWork() {
  try {
    if (!shouldYieldToRenderer()) {
      //