"Internal Server Error" with no other useful information

[heipei]

When starting a local dev server with npm run start and @redocly/cli I don't get any errors, and the server starts up fine, but accessing the site just returns a single string of "Internal Server Error".

To Reproduce I'm not sure how to reproduce this since the same repo works fine on another machine and indeed worked fine on this machine previously. The build on the redocly service works fine.

Expected behavior

I get some kind of debug / verbose output to help me track down the issue.

Logs

> [email protected] start
> npx @redocly/cli preview -p 4002


@redocly/redoc-revel detected in project's 'package.json'
Launching preview of Redoc + Revel enterprise using NPX.

[info] Starting project preview mode.
[info] JavaScript compiled dur="381ms"
[info] File system scan completed dur="8ms"
[info] JavaScript re-compiled dur="242ms"
[info] Preparing search documents and create indexes...
[info] Search indexes created dur="64ms"
[info] Preparing AI search documents...
[info] llms.txt: Generating llms.txt files...
[info] llms.txt: files generated
[info] AI search documents prepared dur="44ms"

───────────────────────────────────────────────────────────────────────────────────────────────────────────

  Previewing with @redocly/[email protected]
  🌐 Preview URL: http://127.0.0.1:4002
  ✅ Status: No errors found
  📄 Total pages: 83
  👀 Watching for changes...

• Site: https://docs.urlscan.io/
• @redocly/redoc-revel 0.122.1
• @redocly/cli 1.34.3
• NodeJS v24.2.0
• MacOS latest