Next.js App Router routes return 404 on Vercel although deployment is Ready

Hi Vercel team,

I'm debugging a Next.js App Router application that works correctly locally but returns 404 for specific routes on Vercel.

Project: nuvexa-tux

GitHub: Rososa2911/Nuxeva-Tux

Main production symptoms:

The production deployment is Ready and Current.
The homepage works.
/auth/login returns 404.
/admin/dashboard returns 404.
Earlier, these routes returned DEPLOYMENT_NOT_FOUND.
The same behavior occurs on the exact deployment URL, not only the production alias.

Evidence:

Vercel Resources explicitly shows: /auth/login /admin/dashboard /admin/agenda /admin/blocks /admin/clients /admin/hours /admin/services /admin/settings /admin/staff
Vercel also shows Routing Middleware with: /admin/:path* /auth/login
The Next.js build manifests contain: /auth/login/page /admin/dashboard/page
The generated files exist: .next/server/app/auth/login/page.js .next/server/app/admin/dashboard/page.js
Local production server works correctly: / -> 307 /auth/login -> 200 /admin/dashboard -> 307 -> /auth/login
No custom basePath, output/export, rewrites, or redirects are configured.
Root Directory is ./.
Framework Preset is Next.js.
Build Command and Output Directory are default.
No vercel.json exists.

Additional tests:

A fresh Vercel project was created from the same GitHub repository and the same route still returned 404.
A Preview branch with middleware removed completely was deployed, and /auth/login still returned 404.
Therefore the issue does not appear to be limited to the original Vercel project or the middleware implementation.
A Node 22 preview was also tested and the route still returned 404.

Current Next.js version: 14.2.35

Could you please check whether there is a Vercel routing/provisioning issue affecting these App Router routes?

The most important point is that:

I can provide deployment IDs and screenshots if needed.