Each Block Lost Reactivity After Navigation

[Kynson]

Hi, I was working a project and encounter some issue with each block when iterating through SvelteSet/ SvelteMap.

Code (simplified example):

<script>
	import {SvelteSet} from 'svelte/reactivity';

	let index = $state(0);

	let initial = $state([0, 1])
	const items = $derived(new SvelteSet(initial));

	function handle() {
		index = (index + 1) % 2;

		items.clear();

		const limit = index === 0 ? 2 : 1

		for (let i = 0; i < limit; i++) {
			items.add(i);
		}
	}

</script>

{#snippet list(value)}
	<div hidden={index !== value}>
		<p>Page: {index}</p>
		{#each items.values() as v (v)}
			{v}
			<br />
		{/each}
	</div>
{/snippet}

<button onclick={handle}>switch page</button>
{@render list(0)}
{@render list(1)}

What I expect the above to do is when the switch page button is clicked, the list should be updated (2 items -> 1 item -> 2 items ...). This works as expected if I visit this page directly. Yet, if I navigate to another page of this app and come back, the list remains with 2 items when I click the button.

May I know why is that? Did I make some mistake?
Demo: https://stackblitz.com/edit/sveltejs-kit-template-default-uhbwxzas (Visit /about directly vs first visit / then /about)

I am using SvelteKit 2.48.0 and Svelte 5.43.8. SSR is disabled for svelte kit

[Kynson]

I figured it out, apparently experimental async is the culprit, removing this option resolves the problem