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.
throw new Error('Expected to find the previous sibling.');
        }
      }
      prevSibling.sibling = newWorkInProgress;
    }
     
     
    const  = returnFiber.Effect;
    if ( !== null) {
      .nextEffect = current;
      returnFiber.Effect = current;
    } else {
      returnFiber.firstEffect = returnFiber.Effect = current;
    }
    current.nextEffect = null;
    current.effectTag = Deletion;
    newWorkInProgress.effectTag |= Placement;
     
    return newWorkInProgress;
  } else {
    throw new Error(
      'Did not expect this call in production. ' +
        'This is a bug in React. Please file an issue.',
    );
  }
}
function beginWork(
  current: Fiber | null,
  workInProgress: Fiber,
  renderExpirationTime: ExpirationTime,