Summary
A gateway or proxy received an invalid response from an upstream server.
When it occurs
Common when a reverse proxy’s backend is down or returns garbage.
Common causes
- Upstream / backend server is down
- Backend returned an invalid response
- Reverse-proxy misconfiguration
- DNS or firewall blocking the upstream
How to fix
- Check the upstream/backend health
- Review reverse-proxy configuration
- Restart the backend service
- Verify upstream DNS and networking