Hello,

I'm experiencing a persistent response decoding issue with JSON API endpoints on Vercel Preview deployments. Static assets and the UI load correctly, but HTTP 200 JSON responses fail to decode in Chrome.

Environment

• Plan: Hobby
• Deployment environment: Preview
• Observed: October 25, 2026, approximately 14:57 KST (05:57 UTC)
• Browser: Chrome on Windows

Observed behavior

GET /api/v1/auth returns:

• HTTP status: 200 OK
• Content-Type: application/json; charset=utf-8
• Content-Encoding: br
• Cache-Control: no-store
• X-Vercel-Cache: MISS

However, Chrome reports:

net::ERR_CONTENT_DECODING_FAILED 200 (OK)

The page displays no JSON body. Another JSON endpoint, /api/records, exhibits the same behavior, while the static dashboard, map clustering, and filters work.

Application authentication is disabled at this stage. The /api/v1/auth endpoint returns fixed JSON without contacting Supabase.

The application uses res.end(JSON.stringify(value)) and does not manually configure compression or Content-Encoding, Content-Length, or Transfer-Encoding headers.

Previous investigation

We reproduced similar behavior in a separate, minimal diagnostic Vercel project:

• Preview HTTP 200 JSON responses failed with Vercel Authentication both enabled and disabled.
• HTTP 422 JSON responses worked.
• Production JSON responses worked in previous tests.
• Preview deployment protection has since been restored.

The current Preview's response bytes under identity/gzip/br negotiations have not yet been independently verified.

Request

Has anyone experienced a similar issue with HTTP 200 JSON responses on Vercel Preview deployments?

I'd appreciate any insights into possible causes or recommended troubleshooting steps.

Thank you.