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

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](vscode-file://vscode-app/c:/Users/seanm/AppData/Local/Programs/Microsoft%20VS%20Code/fcf604774b/resources/app/out/vs/code/electron-browser/workbench/workbench.html))
Workflow uploads static site ([src](vscode-file://vscode-app/c:/Users/seanm/AppData/Local/Programs/Microsoft%20VS%20Code/fcf604774b/resources/app/out/vs/code/electron-browser/workbench/workbench.html)) and API ([api](vscode-file://vscode-app/c:/Users/seanm/AppData/Local/Programs/Microsoft%20VS%20Code/fcf604774b/resources/app/out/vs/code/electron-browser/workbench/workbench.html)) 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 Azure/static-web-apps#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

Start with the GitHub Actions workflow using Azure/static-web-apps-deploy@v1, the api and src locations, and staticwebapp.config.json. Reproduce the deployment and inspect the polling output alongside issue #1760, then determine whether the failure is platform-wide or configuration-specific. Done means the managed .NET 8 isolated Functions deployment succeeds or reports an actionable underlying error.

Written by the indexing model from the issue text.