Occurs in Fiber with multiple instances of the React package (which can't share current owner).
returnFiber: Fiber,
    oldFiber: Fiber | null,
    newChild: any,
    priority: PriorityLevel,
  ): Fiber | null {
    
    const key = oldFiber !== null ? oldFiber.key : null;
    if (typeof newChild === 'string' || typeof newChild === 'number') {
      
      
      
      if (key !== null) {
        return null;
      }
      return updateTextNode(returnFiber, oldFiber, '' + newChild, priority);
    }
    if (typeof newChild === 'object' && newChild !== null) {
      switch (newChild.$$typeof) {
        case REACT_ELEMENT_TYPE: {
          if (newChild.key === key) {
            return updateElement(returnFiber, oldFiber, newChild, priority);
          } else {
            return null;
          }
        }
        case REACT_COROUTINE_TYPE: {
          if (newChild.key === key) {