Next.js sitemap.xml route handler build fails with Invariant error — regression 16.1.7→16.2.0

What this error means

Error: Invariant: failed to find source route /[store]/[lang]/c/sitemap.xml for prerender /[store]/[lang]/c/sitemap.xml is a Vercel failure pattern reported for developers trying to fix next.js build/deployment failure with sitemap.xml route handlers in nested dynamic route groups (regression from 16.1.7 to 16.2.0+). Based on the imported evidence, treat this as a tool-specific troubleshooting page rather than a generic API error.

Why this happens

GitHub issues #94024 and #94041 on vercel/next.js describe a race condition bug in parallel prerendering introduced between Next.js 16.1.7 and 16.2.0. Dynamic force-static sitemap.xml route handlers under nested route groups fail on Vercel but succeed locally. Only consistent on Vercel with 3 parallel build workers. Specific conditions identified (nested groups + sibling [slug] route). Strong commercial impact for production deployments.

Common causes

• GitHub issues #94024 and #94041 on vercel/next.js describe a race condition bug in parallel prerendering introduced between Next.js 16.1.7 and 16.2.0. Dynamic force-static sitemap.xml route handlers under nested route groups fail on Vercel but succeed locally. Only consistent on Vercel with 3 parallel build workers. Specific conditions identified (nested groups + sibling [slug] route). Strong commercial impact for production deployments.

Quick fixes

1. Confirm the exact error signature matches Error: Invariant: failed to find source route /[store]/[lang]/c/sitemap.xml for prerender /[store]/[lang]/c/sitemap.xml.
2. Check the Vercel account, local tool state, and provider configuration involved in the failing workflow.
3. Check the build output, project root, and deployment platform configuration before redeploying.

Platform/tool-specific checks

• Verify the command, editor, extension, or API client that produced the error.
• Compare local settings with CI, deployment, or editor-level settings when the error appears in only one environment.
• Avoid deleting credentials, local model data, or project settings until the failing scope is clear.

Step-by-step troubleshooting

1. Capture the exact error message and the command, editor action, or request that triggered it.
2. Check whether the failure is account/auth, quota/rate, model/provider, local runtime, or deployment configuration.
3. Review the source evidence below and compare it with your environment.
4. Apply one change at a time and rerun the smallest failing action.
5. Keep the working fix documented for the team or deployment environment.

How to prevent it

• Keep provider/tool configuration documented.
• Record non-secret diagnostics such as tool version, provider name, model name, and command path.
• Add a lightweight check before CI or production workflows depend on the tool.

Sources checked

• https://github.com/vercel/next.js/issues/94024
• https://github.com/vercel/next.js/issues/94041

Evidence note: GitHub issues #94024 and #94041 on vercel/next.js describe a race condition bug in parallel prerendering introduced between Next.js 16.1.7 and 16.2.0. Dynamic force-static sitemap.xml route handlers under nested route groups fail on Vercel but succeed locally. Only consistent on Vercel with 3 parallel build workers. Specific conditions identified (nested groups + sibling [slug] route). Strong commercial impact for production deployments.

Related errors

• Deployment

FAQ

What should I check first?

Start with the exact Error: Invariant: failed to find source route /[store]/[lang]/c/sitemap.xml for prerender /[store]/[lang]/c/sitemap.xml text and the smallest action that reproduces it.

Can I ignore this error?

No. Treat it as a failed Vercel workflow until the root cause is understood.

Is this guaranteed to have one fix?

No. The imported evidence supports the troubleshooting path above, but tool behavior can vary by account, plan, version, provider, and local configuration.

How do I know the fix worked?

Rerun the same command, editor action, or request. The fix is working when that action completes without Error: Invariant: failed to find source route /[store]/[lang]/c/sitemap.xml for prerender /[store]/[lang]/c/sitemap.xml.