Static Web Apps: all deployments fail "An unknown exception has occurred" at upload phase — East US 2 slice c2gp-slice-0-eus2-0-ase

[IB-il]

Summary

All deployments to our Azure Static Web Apps in East US 2 fail during the upload phase with the generic An unknown exception has occurred, and no server-side build record is created. Reproduced across three independent environments and against a brand-new clean resource. Production sites remain healthy (serving last-good content) — only new deployments fail.

Deployment slice (common to all failures)

• Slice: c2gp-slice-0-eus2-0-ase (IP 20.96.255.85, port 443)
• TLS cert: CN=*.c2gp-slice-0-eus2-0-ase.p.azurewebsites.net, issuer Microsoft Azure RSA TLS Issuing CA 03 (valid)
• Region: East US 2 · SKU: Standard · (subscription/resource IDs available privately on request)

Reproduced identically in 3 environments, 2 resources

• Local machine (Linux/WSL) and Windows client
• Azure Container Instance in East US 2 (separate Azure-backbone network)
• GitHub Actions runner (official Azure/static-web-apps-deploy@v1)
• Against an existing resource and a brand-new clean Standard SWA
• Minimal one-file index.html payload
• SWA CLI v1.1.10 and v2.0.9 (StaticSitesClient 689a6c1f…) — both fail

What works (rules out client / network / token)

• Token validation succeeds (a bogus token yields a distinct deployment_token provided was invalid)
• TCP ESTABLISHED to the slice; TLS handshake completes (valid MS cert); curl returns HTTP 404 at slice root
• No proxy (Windows WinHTTP = Direct, no proxy env vars)
• Generic Azure Blob Storage read/write works fine from the same machine

Symptom detail

Fails right after Preparing deployment… DeploymentId: <guid>. The Windows client (verbose) reaches Determined default file to be: index.html, then throws. The inner exception is swallowed by the client's top-level handler. The portal's "Retrieve deployment error messages" shows nothing (no build record). Affected env stuck in Uploading; the new clean resource stuck in WaitingForDeployment.

Sample failed Deployment IDs

• 936618cb-e872-45e6-8e35-f5de9b91dccb (CLI v1.1.10)
• cdf7b2fa-426d-4373-88f4-ca43cd354a6d (CLI v2.0.9)
• 2cc377ef-8425-4f5e-8173-aeb6d7df9a13 (GitHub Actions)

Ask

1. Investigate the East US 2 deployment slice/backend c2gp-slice-0-eus2-0-ase.
2. Surface the swallowed inner exception behind the generic CLI message.
3. Confirm when deployments through this slice are healthy again.

Happy to provide subscription/resource IDs privately to a Microsoft engineer.