regression: `#await` block does not resolve `Promise` from `+page.server.ts` if loader contains another `await`

[firatciftci]

Describe the bug

I have a page whose +page.server.ts contains two calls to my database; one to get SEO data to be used inside <svelte:head>, and another to be displayed on the page. The former is awaited inside the loader function, returning just a string, which is then passed along to the client/SSR. The latter, though, is not awaited inside the loader, and so its promise is passed along to the +page.svelte file to be awaited inside an {#await} block. Starting with SvelteKit version 2.37.1 (probably after this PR: #14298), there appears to be a regression where the {#await} block (almost) never resolves the promise on +page.svelte; this could be a race condition, as the promise is rarely resolved, but 9 times out of 10, the loading state inside the {#await} block simply hangs.

If you remove the awaited function call inside the +page.server.ts file (and thus returning only the Promise data), then the issue goes away, but I have my whole application set up in this exact manner, so doing this is not a workaround/fix that I can apply.

Reproduction

Create a +page.svelte file that is set up to read the data from $props(); data.seo is passed inside relevant SEO fields inside <svelte:head> directly, and data.items is a Promise that is to be resolved inside an {#await} block, whose content will be displayed on the page.

The former step should work properly (i.e., the <title>, etc. should update accordingly), but the latter step should never resolve (9 times out of 10).

Logs

System Info

System:
    OS: macOS 26.0
    CPU: (14) arm64 Apple M4 Pro
    Memory: 115.22 MB / 24.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 22.19.0 - ~/.local/state/fnm_multishells/10602_1758321273340/bin/node
    npm: 11.6.0 - ~/.local/state/fnm_multishells/10602_1758321273340/bin/npm
    pnpm: 10.17.0 - ~/Library/pnpm/pnpm
    bun: 1.2.20 - ~/.bun/bin/bun
    Watchman: 2025.09.08.00 - /opt/homebrew/bin/watchman
  Browsers:
    Chrome: 140.0.7339.134
    Safari: 26.0
  npmPackages:
    @sveltejs/adapter-node: ^5.3.2 => 5.3.2
    @sveltejs/kit: ^2.42.2 => 2.42.2
    @sveltejs/vite-plugin-svelte: ^6.2.0 => 6.2.0
    rolldown-vite:  7.1.11
    svelte: ^5.39.3 => 5.39.3

Severity

blocking all usage of SvelteKit

Additional Information

No response

[firatciftci]

Here is a code example of the setup I have described above:

// src/routes/item/[slug]/+page.server.ts

import type { PageServerLoad } from "./$types";
import { getItemSeo } from "$lib/server/db/queries/get-item-seo";
import { getItem } from "$lib/server/db/queries/get-item";

export const load: PageServerLoad = async ({ params }) => {
  const item = getItem(params.slug); // not awaited, returns a Promise
  const seoData = await getItemSeo(params.slug); // awaited on the server

  return {
    item,
    seo: {
      title: seoData.name,
      description: seoData.note,
    },
  };
};

And the page itself:

<script lang="ts">
  import type { PageProps } from "./$types";
  import LoadingItem from "$lib/components/loading/item.svelte";
  import Item from "$lib/components/item/index.svelte";

  let { data }: PageProps = $props();
</script>

<svelte:head>
  <title>{data.seo.title}</title>
  <meta name="description" content={data.seo.description} />
</svelte:head>

<main class="py-2 sm:py-3">
  {#await data.item}
    <LoadingItem />
  {:then item}
    <Item {item} />
  {/await}
</main>

As explained, the SEO data is passed over without any issues, but the data.item is not (the Promise never resolves).

[PatrickG]

Sorry for the late response.
I couldn't reproduce this issue with the latest sveltekit version.
Can you please provide a minimal reproduction?
Does it only happen when hitting that route directly (reload) or with client-side navigation as well?

[firatciftci]

I was finally able to create a minimal example with a reproduction; you can see it here: https://github.com/firatciftci/sveltekit-await-issue-reproduction.

One thing was missing from my example above: I also have a root +layout.server.ts with a function that passes a Promise to the root layout page, which then gets passed along to a header component to be awaited and displayed there. Almost always, the layout/header Promise resolves faster than the other page data Promises, which then causes the page Promises to never resolve. Downgrading @sveltejs/kit to version 2.37.0 resolves this issue (i.e., this issue has been present ever since then).

I have created mock data utilities where playing with the order of Promises (via changing the timeout values) will change the outcome. Specifically, if you make the layout Promise take longer to resolve, then the page Promises also resolve successfully.

Please let me know if there is anything else that you need from me! Thank you for taking a look at this.

[firatciftci]

Also important to note that client-side navigation does not exhibit this issue, only a reload.

[PatrickG]

Thanks, that was very helpful.