Occurs in Fiber with multiple instances of the React package (which can't share current owner).
returnFiber: Fiber,
    current: Fiber | null,
    portal: ReactPortal,
    priority: PriorityLevel,
  ): Fiber {
    if (
      current === null ||
      current.tag !== HostPortal ||
      current.stateNode.containerInfo !== portal.containerInfo ||
      current.stateNode.implementation !== portal.implementation
    ) {
      
      const created = createFiberFromPortal(
        portal,
        returnFiber.internalContextTag,
        priority,
      );
      created.return = returnFiber;
      return created;
    } else {
      
      const existing = useFiber(current, priority);
      existing.pendingProps = portal.children || [];
      existing.return = returnFiber;
      return existing;
    }
  }
  function updateFragment(