React Router app cannot be accessed in recent Vercel deployments

[GregoryZeng]

Hi,
My React Router project recently deploys successfully on Vercel, but the deployed site shows a 500 error when accessed:

500: INTERNAL_SERVER_ERROR
Code: FUNCTION_INVOCATION_FAILED
ID: iad1::9mzx2-1761741964954-b9ba1575dd91

The server logs display this message:

Cannot find module '/var/task/node_modules/@mjackson/node-fetch-server/dist/node-fetch-server.cjs'
Did you forget to add it to "dependencies" in `package.json`?
Node.js process exited with exit status: 1. The logs above can help with debugging the issue.

However, this error occurs even though I haven’t changed anything related to dependencies. The latest code runs normally in my local machine.

To verify, I reproduced the issue using the official React Router boilerplate template and can see the same “cannot find module” error in the logs.
Code: React Router Boilerplate
Deployed: https://test-rr-one.vercel.app/