Azure Portal does not show logs and invocations for manual trigger of timer functions in .NET isolated worker with OpenTelemetry mode

#### Check for a solution in the Azure portal
Checked "Diagnose and solve problems" — no relevant solutions found for this issue.

#### Investigative information
- **Timestamp:** April 2026 (ongoing, reproducible)
- **Function App version:** Azure Functions v4, .NET 10 isolated worker
- *Region*: *West Europe*

#### Repro steps
1. Create a .NET 10 isolated worker Azure Function with a timer trigger (`0 */5 * * * *`)
2. Install nuget packages
```csharp

```
3. Configure OpenTelemetry-based Application Insights in `Program.cs`:
```csharp
var builder = FunctionsApplication.CreateBuilder(args);

builder.Services
.AddOpenTelemetry()
.UseFunctionsWorkerDefaults()
.UseAzureMonitorExporter();

builder.Build().Run();

```

3. Set "telemetryMode": "OpenTelemetry" in host.json
```json
{
"version": "2.0",
"telemetryMode": "OpenTelemetry"
}
```
4. Deploy to Azure
5. Wait for timer to fire, or trigger manually via admin API: POST /admin/functions/TimerFunction with body {"input": ""}
6. Open the Portal - check "Code + Test" log stream and "Monitor" > invocation list

**Expected behavior**
- Portal "Code + Test" log stream should display function execution logs in real time
- Portal Monitor blade should show invocation entries with invocation IDs
- Application Insights should receive full telemetry (traces, dependencies, exceptions) from the function execution
- Behavior should be identical regardless of whether the function is triggered by schedule, Portal "Run" button, or admin API (POST /admin/functions/TimerFunction)

**Actual behavior**
When triggered manually from the Azure Portal "Run" button:
- The function does execute — confirmed by side effects (e.g., file processing)
- Portal "Code + Test" log stream shows nothing
- Portal Monitor blade invocation list is empty — no invocation entry, no invocation ID
- Application Insights receives only the HTTP request to /admin/functions/TimerFunction, but no traces, dependencies, or exceptions from the function execution itself

When triggered via Postman/Curl (same admin API endpoint, same payload):
- All of the above work correctly — logs stream in the Portal, invocations appear in Monitor, and full telemetry is visible in Application Insights

**Known workarounds**
- Instead of using the Portal "Run" button, trigger the function manually by sending a POST request directly to the admin API:
```
POST https://.azurewebsites.net/admin/functions/
Content-Type: application/json
x-functions-key:
{
"input": ""
}
```