Failed to deploy Azure Functions - .NET 8.0 Isolated managed Functions deployment failing since June 22, 2026

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Describe the bug

Azure Static Web Apps deployment consistently fails with "Failed to deploy the Azure Functions" during the polling phase (~17-22 seconds after artifact upload), despite build succeeding. The failure occurs for a .NET 8.0 isolated Functions API hosted on managed SWA (Free tier). This appears to be the same platform-wide issue reported in #1760 (Next.js deployment failures since June 8, 2026).

To Reproduce

Steps to reproduce the behavior:

Commit to master branch with GitHub Actions CI workflow configured
Workflow checks out repo, builds .NET 8.0 isolated Functions API (source location: api)
Workflow uploads static site (src) and API (api) via Azure/static-web-apps-deploy@v1
Upload completes successfully within 3-10 seconds
Deployment polling begins and runs for ~17 seconds
Polling fails with: "Deployment Failure Reason: Failed to deploy the Azure Functions."
No additional error details available in GitHub Actions logs or Azure Activity Log
Configuration Files

GitHub Actions Workflow (primary):

• name: Build And Deploy
  id: builddeploy
  uses: Azure/static-web-apps-deploy@v1
  continue-on-error: true
  with:
  app_location: "src"
  api_location: "api"
  output_location: ""

[staticwebapp.config.json] (with managed Functions):

{
"platform": {
"apiRuntime": "dotnet-isolated:8.0"
},
"routes": [
{
"route": "/api/*",
"allowedRoles": ["anonymous"]
}
]
}

API Configuration (Bicep):

API settings provisioned via Microsoft.Web/staticSites/config@2022-09-01 (appsettings)
Environment variables: GRAPH_TENANT_ID, GRAPH_CLIENT_ID, GRAPH_CLIENT_SECRET, GRAPH_SENDER_UPN, MAIL_TO, TURNSTILE_*
No separate Function App resource (using SWA managed Functions only)
Expected behavior

Deployment should complete successfully with both static site and managed Functions API active. Polling should complete within the 90-second window and either succeed or fail with actionable error details.

Environment

OS: Linux (GitHub Actions runner, ubuntu-latest)
SWA Tier: Free
Region: uksouth
API Runtime: .NET 8.0 isolated
Build: Succeeds every time (verified with diagnostic build logs)
API Package Size: 36.86 MB (well under 256MB limit)
Deployment Timeline

Last successful deployment: June 20, 2026
First failure: June 22, 2026 (~3:53 PM UTC)
Framework: Custom .NET 8.0 isolated Functions
No code changes to deployment logic between success and failure

Error Logs
Status: InProgress. Time: 1.179581(s)
Status: Failed. Time: 17.1468984(s)
Deployment Failed :(
Deployment Failure Reason: Failed to deploy the Azure Functions.

Build phase: ✅ SUCCESS (Oryx detected and compiled .NET 8.0.26)
Polling phase: ❌ FAILURE (at ~17 seconds)
No underlying error details in Activity Log
Related Issues

This appears identical to #1760 (Next.js 14 deployment failing since June 8, 2026):

Same failure timing (30-33 seconds polling)
Same error message
Platform-level regression starting June 8, 2026
Affects multiple frameworks

Additional context
Workaround implemented: Added retry logic to deploy action to handle transient failures
Retry condition: if: steps.builddeploy.outcome == 'failure'
First attempt fails, retry also fails (same error at same timing)
Code/configuration verified correct per Microsoft Learn documentation
No custom build steps or non-standard paths used