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**Do you want to request a *feature* or report a *bug*?**
Not sure if its a bug or a feature request.

**What is the current behavior?**
The component given as a fallback to Suspense is remounted each time a lazy child resolves.

https://codesandbox.io/s/z6v6x3n1np
This example shows how a fallback component, which counts up, is mounted more than once.

**What is the expected behavior?**
The fallback is mounted once and is only unmounted when all lazy children are resolved.
In the example the counter would run up to 9.

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

'Should have next effect. This error is likely caused by a bug ' +
          'in React. Please file an issue.',
      );
      captureCommitPhaseError(nextEffect, error);
      
      if (nextEffect !== null) {
        nextEffect = nextEffect.nextEffect;
      }
    }
  }
  stopCommitHostEffectsTimer();
  resetAfterCommit(root.containerInfo);
  
  
  
  
  root.current = finishedWork;
  
  
  
  
  nextEffect = firstEffect;
  startCommitLifeCyclesTimer();
  while (nextEffect !== null) {
    let didError = false;
    let error;
    if (__DEV__) {
      invokeGuardedCallback(
        null,
        commitAllLifeCycles,