No Telemetry in IOT Central for the majority of devices connected, but Command Request Response still working.

Question

No Telemetry in IOT Central for the majority of devices connected, but Command Request Response still working.

Michael Woods 0

Hello,

I am trying to setup a fleet of IOT devices using IOT Central. I have been using it with samples fairly successfully for more than a year.

Yesterday I witnessed the following cascade of problems. A couple of the devices on the network stopped pushing any telemetry data to IOT Central as viewable via the "Raw Data" view. Then a couple of hours later more units, roughly 6 units of the 14 I have connected, they also stopped showing telemetry data in the "Raw Data" view. Then a couple of hours later more still stopped showing telemetry data, down to the point where I only had 2 units pushing telemetry still.

As part of my investigation I checked that all the units in the field were still pushing data without errors and they were operating as they normally would. I verified with a test device I can easily debug that it was definitely pushing to IOT Central without throwing any Exceptions.

I was still able to send Commands to the devices and have the devices responded correctly and that was visible on the Raw Data view.

I looked at the Metrics for the IOT Central application in Azure to check the number of messages sent from device to cloud was consistent with what it was before the issue.

I can see that the export I had setup for pushing to Blob storage was also showing that it was not receiving any data.

I am really concerned about this outage, as the failure mechanism is completely opaque in addition all the data that was supposedly sent appears lost now that they system has somewhat "fixed" itself.

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2 answers

Your answer

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Answer 1

Hi Michael Woods,

Thanks for posting your question. I understand how frustrating it can be when most devices stop sending telemetry to IoT Central. Here are a few checks and troubleshooting steps that usually help in this situation.

Please verify that the telemetry your devices are sending matches the device template. You can use the Azure CLI command az iot central diagnostics validate-messages to confirm if there are any schema or field mismatches. If the incoming data does not align with the template, IoT Central may not display the telemetry correctly.
Open the Raw Data view for one of the affected devices. This helps you see whether any telemetry is reaching IoT Central at all. In many cases, malformed JSON or unmodeled telemetry fields cause the data to be ignored or displayed incorrectly.
Check the device connectivity. Even if devices appear connected, it’s useful to run az iot central diagnostics monitor-events to confirm that the messages are actually arriving at the backend. If you are using IoT Edge, please ensure the runtime is updated, as older versions sometimes cause issues with telemetry forwarding.
if everything looks correct but telemetry disappears intermittently and returns later, it may be a transient service-side issue. In such cases, capturing logs and share timestamp details can help identify backend-related problems.

I hope this clears things up! Please let me know if there are any remaining questions or additional details, I can help with, I’ll be glad to provide further clarification or guidance.

Thankyou!

Anshika Varshney 15,625 Reputation points Microsoft External Staff Moderator

2025-12-01T13:16:26.42+00:00

Hi Michael Woods,

I’ve converted comment into an answer, could you please take a moment to mark it as Accepted? This helps others in the community with the same question find the solution more easily.
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Answer 2

It seems you're experiencing issues with telemetry data not being sent from multiple IoT devices to Azure IoT Central, while command requests are still functioning. Here are some steps you can take to troubleshoot the situation:

Check Device Connectivity: Ensure that all devices are still connected and have network access. You can verify the provisioning status of each device using the Azure CLI command:
```
   az iot central device registration-info --app-id <iot-central-app-id> --device-id <device-name>
```
This will help you identify if any devices are blocked, unapproved, or unassigned.
Validate Telemetry Data: Use the following command to validate the telemetry being sent from your devices:
```
   az iot central diagnostics validate-messages --app-id <iot-central-app-id> --device-id <device-name>
```
This will help you check if the telemetry data format is correct and matches the device template.
Review Raw Data: In IoT Central, navigate to the Raw data view for the affected devices. This view can provide insights into any unmodeled data or malformed JSON that may be causing issues with telemetry data not appearing.
Check for Unmodeled Data: If the Unmodeled data column shows data from the device that doesn't match any property or telemetry definitions in the device template, you may need to update the device firmware or create a new device template.
Monitor Events: Use the command to monitor events and see if the telemetry is being sent but not displayed:
```
   az iot central diagnostics monitor-events --app-id <iot-central-app-id> --device-id <device-name>
```
Check IoT Edge Version: If you are using IoT Edge, ensure that you are using version 1.2.4 or later, as earlier versions may cause telemetry from components to display incorrectly.

If the telemetry data is still not appearing after these checks, consider reviewing the logs from your devices for any error codes that may indicate issues with the data transmission.

References: