Intermittent IoT Device Connection to Azure IoT Hub

Question

Dear Microsoft Azure Support Team,

I am reaching out to kindly request your assistance in identifying the exact cause of an intermittent connection issue between my IoT device and the Azure IoT Hub.

I am currently developing firmware for a board called LilyGo, which includes an ESP32-WROVER microcontroller and a SIMCOM A7670SA modem.

At the moment, for example, the device is successfully connected; however, at any given time, the modem disconnects unexpectedly. Even if I revert to the original firmware code (without any modifications), the modem often fails to reconnect afterward.

My initial suspicion is that the issue may be related to the SAS token expiration, but after conducting several tests — generating new tokens and attempting reconnection — all attempts have failed.

To give you an idea, I haven’t changed a single line of code since last Friday, and today, after simply updating the SAS token, the board connected successfully again. At this moment, the modem is connected and functioning normally.

Do you understand what might be happening? For some reason, the modem suddenly loses connection and is unable to reconnect for a period of time. Then, after a few days, it reconnects successfully without any code changes.

I need to understand what is causing this behavior. My impression is that the IoT Hub, after a few failed connection attempts, starts rejecting further connections from the device, reporting a connection failure — even when using a valid, non-expired SAS token.

Could you please help me understand what is happening and how I can resolve this issue?

Device Information:

• Device ID: dispositivo_beta01-4G
• Host name: REDACTEDATSupportSide__.azure-devices.net__
• Microsoft Account: REDACTEDATSupportSide__@outlook.com__

P.S.: Attached to this message are two logs to help analyze the issue: the first shows a successful connection, and the second shows an unsuccessful connection after the modem disconnects and is unable to reconnect, even when reverting to the original firmware code.

Thank you very much for your support.

20251031 Log ConectaAzure - COMErros.txt

20251031 Log ConectaAzure - semErros.txt