Occurs in Fiber with multiple instances of the React package (which can't share current owner).
returnFiber: Fiber,
    currentFirstChild: Fiber | null,
  ): null {
    if (!shouldTrackSideEffects) {
      
      return null;
    }
    
    
    let childToDelete = currentFirstChild;
    while (childToDelete !== null) {
      deleteChild(returnFiber, childToDelete);
      childToDelete = childToDelete.sibling;
    }
    return null;
  }
  function mapRemainingChildren(