I tried multiple approaches, but eventually found that the root cause was a "Page Not Found" error.

In my case, the route name in the code was sign-in, but on GitHub, I had accidentally pushed it as Sign-in. Since Next.js is case-sensitive with routes, this mismatch caused the deployed version on Vercel to fail.

After changing the route name to all lowercase (sign-in) in the main branch and redeploying, everything started working fine