{"ERRORCODE": 9999, "Message": "Session terminated.", "InnerException": null}

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{"ERRORCODE": 9999, "Message": "Session terminated.", "InnerException": null}

Dustin Chavez 80

I am getting {"ERRORCODE": 9999, "Message": "Session terminated.", "InnerException": null} when I am making many calls of a function app function through an event grid trigger. I notice I can successfully upload around 1 file a second without issues, however, as I upload more, the errors become more frequent with more files being concurrently added. Any guidance would be greatly appreciated. Thank you. Screenshot 2025-11-17 124537

Dustin Chavez 80

Hello @Pravallika KV I have implemented this dynamicconcurrencyenabled into my function app host.json file, however I am still experiencing this issue with increased concurrency. Is there somewhere else within the azure settings that need to be configured in order to apply this?

{
  "version": "2.0",
  "functionTimeout": "-1",
  "logging": {
    "applicationInsights": {
      "samplingSettings": {
        "isEnabled": true,
        "maxTelemetryItemsPerSecond": 5
      }
    }
  },
  "managedDependency": {
    "enabled": true
  },"retry": {
    "strategy": "exponentialBackoff",
    "maxRetryCount": 3,
    "minimumInterval": "00:00:10",
    "maximumInterval": "00:10:00"
  },
  "extensionBundle": {
    "id": "Microsoft.Azure.Functions.ExtensionBundle",
    "version": "[4.*, 5.0.0)"
  },"concurrency": {
    "dynamicConcurrencyEnabled": true
  }
}

Pravallika KV 3,565 Microsoft External Staff Moderator

@Dustin Chavez ,

Have you tried implementing retry policies or utilize Application Insights to gather more data about the errors?

Introduce a queue layer and use the recommended high-throughput pattern:

The queue buffers events, so your Function App processes them at a safe rate.
Queue triggers support dynamic concurrency, batching, and automatic retry.
This avoids overload from Event Grid bursts and removes “session terminated” failures.

Event Grid → Storage Queue → Function (queue-triggered)

Set batchSize and newBatchThreshold in host.json to control concurrency:

{
  "version": "2.0",
  "functionTimeout": "-1",
  "logging": {
    "applicationInsights": {
      "samplingSettings": {
        "isEnabled": true,
        "maxTelemetryItemsPerSecond": 5
      }
    }
  },
  "managedDependency": {
    "enabled": true
  },
  "retry": {
    "strategy": "exponentialBackoff",
    "maxRetryCount": 5,
    "minimumInterval": "00:00:10",
    "maximumInterval": "00:05:00"
  },
  "extensionBundle": {
    "id": "Microsoft.Azure.Functions.ExtensionBundle",
    "version": "[4.*, 5.0.0)"
  },
  "extensions": {
    "queues": {
      "batchSize": 16,
      "newBatchThreshold": 8,
      "maxDequeueCount": 5,
      "visibilityTimeout": "00:01:00",
      "messageEncoding": "base64"
    }
  },
  "concurrency": {
    "dynamicConcurrencyEnabled": true,
    "snapshotPersistenceEnabled": true
  }
}

Pravallika KV 3,565 Reputation points Microsoft External Staff Moderator

2025-12-11T18:01:28.14+00:00

Hi @Dustin Chavez , following up to see if you had a chance to check the above provided information was helpful. If you have any further queries do let us know.
Dustin Chavez 80 Reputation points

2025-12-11T20:36:22.6933333+00:00

Hi @Pravallika KV , it turns out this error was coming from our internal API rather than an error from the function app. Sorry about that, thank you for looking into this.
Pravallika KV 3,565 Reputation points Microsoft External Staff Moderator

2025-12-11T20:40:35.25+00:00

@Dustin Chavez , Thanks for the confirmation. I have posted the answer. If this answers your query, please do click Accept Answer and Yes for was this answer helpful and upvote it 👍. If you have any further query do let us know.

Answer accepted by question author

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Dustin Chavez 80 Reputation points

2025-12-10T15:31:02.3066667+00:00

Hello @Pravallika KV I have implemented this dynamicconcurrencyenabled into my function app host.json file, however I am still experiencing this issue with increased concurrency. Is there somewhere else within the azure settings that need to be configured in order to apply this?

{ "version": "2.0", "functionTimeout": "-1", "logging": { "applicationInsights": { "samplingSettings": { "isEnabled": true, "maxTelemetryItemsPerSecond": 5 } } }, "managedDependency": { "enabled": true },"retry": { "strategy": "exponentialBackoff", "maxRetryCount": 3, "minimumInterval": "00:00:10", "maximumInterval": "00:10:00" }, "extensionBundle": { "id": "Microsoft.Azure.Functions.ExtensionBundle", "version": "[4.*, 5.0.0)" },"concurrency": { "dynamicConcurrencyEnabled": true } }
Pravallika KV 3,565 Reputation points Microsoft External Staff Moderator

2025-12-10T18:43:05.66+00:00

@Dustin Chavez ,

Have you tried implementing retry policies or utilize Application Insights to gather more data about the errors?

Introduce a queue layer and use the recommended high-throughput pattern:

The queue buffers events, so your Function App processes them at a safe rate.

Queue triggers support dynamic concurrency, batching, and automatic retry.

This avoids overload from Event Grid bursts and removes “session terminated” failures.

Event Grid → Storage Queue → Function (queue-triggered)

Set batchSize and newBatchThreshold in host.json to control concurrency:

{ "version": "2.0", "functionTimeout": "-1", "logging": { "applicationInsights": { "samplingSettings": { "isEnabled": true, "maxTelemetryItemsPerSecond": 5 } } }, "managedDependency": { "enabled": true }, "retry": { "strategy": "exponentialBackoff", "maxRetryCount": 5, "minimumInterval": "00:00:10", "maximumInterval": "00:05:00" }, "extensionBundle": { "id": "Microsoft.Azure.Functions.ExtensionBundle", "version": "[4.*, 5.0.0)" }, "extensions": { "queues": { "batchSize": 16, "newBatchThreshold": 8, "maxDequeueCount": 5, "visibilityTimeout": "00:01:00", "messageEncoding": "base64" } }, "concurrency": { "dynamicConcurrencyEnabled": true, "snapshotPersistenceEnabled": true } }
Pravallika KV 3,565 Reputation points Microsoft External Staff Moderator

2025-12-11T18:01:28.14+00:00

Hi @Dustin Chavez , following up to see if you had a chance to check the above provided information was helpful. If you have any further queries do let us know.
Dustin Chavez 80 Reputation points

2025-12-11T20:36:22.6933333+00:00

Hi @Pravallika KV , it turns out this error was coming from our internal API rather than an error from the function app. Sorry about that, thank you for looking into this.
Pravallika KV 3,565 Reputation points Microsoft External Staff Moderator

2025-12-11T20:40:35.25+00:00

@Dustin Chavez , Thanks for the confirmation. I have posted the answer. If this answers your query, please do click Accept Answer and Yes for was this answer helpful and upvote it 👍. If you have any further query do let us know.

Answer 1

Pravallika KV 3,565 Microsoft External Staff Moderator

Hi @Dustin Chavez ,

Thanks for the confirmation. Glad you were able to figure out the issue.

Upon investigating further, it turned out this error was coming from the internal API rather than an error from the function app.

Hope it helps!

Please do not forget to click "Accept the answer” and Yes, this can be beneficial to other community members.

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If you have any other questions, let me know in the "comments" and I would be happy to help you.

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{"ERRORCODE": 9999, "Message": "Session terminated.", "InnerException": null}

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