<!--
  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*?**
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

_current,
  workInProgress,
  elementType,
  updateExpirationTime,
  renderExpirationTime,
) {
  if (_current !== null) {
    
    
    
    
    _current.alternate = null;
    workInProgress.alternate = null;
    
    workInProgress.effectTag |= Placement;
  }
  const props = workInProgress.pendingProps;
  
  
  cancelWorkTimer(workInProgress);
  let Component = readLazyComponentType(elementType);
  
  workInProgress.type = Component;
  const resolvedTag = (workInProgress.tag = resolveLazyComponentTag(Component));