TypeScript - Why are global exported variables undefined in some contexts when they were set in another context?

I'm trying to have a shared store of global variables in a Vue.js application. Since only some properties are relevant to the state of the actual application, only those are wrapped in a Vue reactivity Ref object. However, those that are not wrapped by a Ref do not have consistent values across different contexts/scopes. Here's example code that represents what I'm trying to do:

Store.ts:

export interface Store {
  container: Container | undefined;
  reactiveProperty: Ref<Property | undefined>;
  getContainer: () => Container | undefined;
  getProperty: () => Property | undefined;
}

function useStore(): Store {
  let container: Container | undefined = undefined;
  const reactiveProperty: Ref<Property | undefined> = ref();
  

  function getContainer() {
    return container;
  }

  function getProperty() {
    return property.value;
  }

  return {
    container,
    reactiveProperty,
    getContainer,
    getProperty
  };
}

const store = useStore();
export {store};

App.ts:

import {store} from '@/store';

let {container, reactiveProperty, getContainer, getProperty} = store;

onMounted(() => {
  container = new Container();
  reactiveProperty.value = new Property('foo');
  const savedContainer = getContainer(); //savedContainer is undefined
  const savedProperty = getProperty(); //savedProperty has the correct value
});

I've also tried wrapping all member accesses into getters and setters, as well as directly accessing the properties using store.container. The latter works when used in different parts of the app, but a call to getContainer() would still return undefined.

What causes this and how can I fix it?