_payload.json-isr 404 on ISR routes deployed to Vercel

Environment

Nuxt: 4.3.1
Nitro: 2.13.1
Deployment target: Vercel
Node.js: 22.x

Reproduction

routeRules: {
'/cookies': { isr: 3600 },
}.
The issue is a also tested it on a new nuxt project. And it does work. The single page where i enabled isr https://www.hetvitaliteitsplatform.nl/cookies. you can observe the error. modules i use modules: [
"@nuxtjs/seo",
"@nuxt/eslint",
"@nuxt/image",
"@nuxt/ui",
// Content module automatically integrates with sitemap
"@nuxt/content",
"@nuxtjs/supabase",
"nuxt-security",
"@nuxt/hints",
"nuxt-lettermint",
"@nuxt/scripts",
"nuxt-ai-ready",
"@nuxt/a11y",
],

Describe the bug

Deploy to Vercel. Navigate to /cookies (both direct navigation and client-side navigation).

Describe the bug

When navigating to an ISR-cached route, Nuxt attempts to fetch /_payload.json-isr for the page (e.g. /cookies/_payload.json-isr). This request returns a 404:

json
{
"error": true,
"url": "https://example.com/cookies/_payload.json-isr",
"statusCode": 404,
"statusMessage": "Page not found: /cookies/_payload.json-isr",
"message": "Page not found: /cookies/_payload.json-isr",
"data": { "path": "/cookies/_payload.json-isr" }
}
Expected behavior

The _payload.json-isr file should be served correctly, or Nuxt should handle the 404 gracefully without logging an error.

Actual behavior

The page loads correctly (ISR cache hit confirmed via x-vercel-cache: HIT), but a 404 network error for _payload.json-isr is logged in the browser console on every navigation to the ISR route. No visible impact to the user, but the error is noisy and may mask real issues.

Additional context

No response

Logs

Start by reproducing the deployed /cookies ISR route and inspect the browser request for /cookies/_payload.json-isr, including its response and the x-vercel-cache status. Trace the ISR payload request handling in Nitro/Nuxt and verify the fix by navigating directly and client-side without a 404 console error.