Repro case with a master build: https://codesandbox.io/s/stoic-mcnulty-dhygf?file=/src/App.js:668-703

Expected: we see content after a second.
Actual: fallback never resolves.

This happens in a sequence of:

1. Normal update
   - which suspends
2. Idle update
   - which also suspends
3. An unrelated normal update immediately followed by a ping (so they're batched)
   - here, we decide to stay on fallback, but should've shown the content

If you remove `_setVersion(v => v + 1);` on line 44 then the issue goes away.
if (current !== null) {
      
      
      
      
      current.alternate = null;
      workInProgress.alternate = null;
      
      workInProgress.effectTag |= Placement;
    }
    
    constructClassInstance(workInProgress, Component, nextProps);
    mountClassInstance(
      workInProgress,
      Component,
      nextProps,
      renderExpirationTime,
    );
    shouldUpdate = true;
  } else if (current === null) {
    
    shouldUpdate = resumeMountClassInstance(
      workInProgress,
      Component,
      nextProps,
      renderExpirationTime,
    );
  } else {
    shouldUpdate = updateClassInstance(
      current,