kit: Defer not working properly when multiple promises are returned

Describe the bug

I’ve tryed the new defer api with vercel edge functions and when a single promise is returned it works as intended. However when you return multiple promises things get’s messy quickly.

For example

const wait = (ms) => new Promise((r) => setTimeout(r, ms));

async function getBlog() {
	await wait(2000);
	return 'A cool blog post';
}

async function getComments() {
	await wait(4000);
	return ['Very cool', 'Super', 'Fantastic'];
}

async function getRecommended() {
	await wait(1000);
	return ['Another post', 'Suh interesting'];
}

async function getFail() {
	await wait(8000);
	throw new Error('Dang!');
}

export async function load() {
	const recommended = getRecommended();
	const comments = getComments();
	const fail = getFail();
	const blog = await getBlog();
	return {
		blog,
		defer: {
			recommended,
			comments,
			fail
		}
	};
}

this configuration correcly wait 2 seconds before showing the page. The recommended shows a sliver of loading state to than resolve immediately however for getComments and getFail the loading state perpetrate until both of them resolve at the same time. When i was trying this at the beginning i saw the same kind of result with only getRecommended + getComments (in this case getRecommended that should already be resolved was persisting in the loading state for a couple of seconds).

https://user-images.githubusercontent.com/26281609/220394130-afd142cd-f182-4190-97b0-16ca99f055c0.mp4

Reproduction

You can see the live version of this on vercel.

You can see the code on my github repo and edit the code on stackblitz

Logs

No logs

System Info

System:
  OS: Linux 5.0 undefined
  CPU: (8) x64 Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
  Memory: 0 Bytes / 0 Bytes
  Shell: 1.0 - /bin/jsh
Binaries:
  Node: 16.14.2 - /usr/local/bin/node
  Yarn: 1.22.19 - /usr/local/bin/yarn
  npm: 7.17.0 - /usr/local/bin/npm
npmPackages:
  @sveltejs/adapter-auto: ^2.0.0 => 2.0.0 
  @sveltejs/adapter-vercel: ^2.0.4 => 2.0.4 
  @sveltejs/kit: ^1.5.0 => 1.8.3 
  svelte: ^3.54.0 => 3.55.1 
  vite: ^4.0.0 => 4.1.3

Severity

blocking an upgrade

Additional Information

No response