iOS SmartThings commissioning fails (39-900) when using MatterLightbulb in multi-sensor example on XIAO MG24

[Simone Genovese (simonegenovese)]

Hello Tamas Jozsi (@silabs-bozont) and all,
first of all thank you for the great work on the Arduino Matter support, it has been extremely helpful.

I am working with Seeed Studio XIAO MG24 using the Silicon Labs Arduino core and Matter libraries.

I noticed the following behavior related to multi-endpoint / multi-device sketches on iOS through SmartThings.

Working case

The official example
https://github.com/SiliconLabs/arduino/blob/main/libraries/Matter/examples/matter_sensor_multiple/matter_sensor_multiple.ino

works as expected when commissioning the device, with SmartThings on iOS.

In particular, combinations like:
• MatterTemperature
• MatterHumidity

commission correctly.

And I can see both temperature and humidity as a single device.

Failing case

If I take the same example and replace MatterHumidity with MatterLightbulb, keeping everything else unchanged, the behavior changes:
• It successfully commission the Device but recognise only one (the Lightbulb)
• After completing the setup I'll see only the Lightbulb and no Temperature

Important notes:
• Using only one device (only MatterLightbulb or only MatterTemperature) works correctly
• The failure happens when combining any another topology of devices in the same sketch (I tried Switch, LightBulb, etc...) on SmartThings
• On Home app is working properly:

•	A full factory reset / decommission of the device is performed between attempts

Questions

1.	Is mixing MatterLightbulb with other device types in a single Node currently supported in the Arduino Matter API?
2.	Are there additional requirements for endpoint numbering, device type declaration, or Descriptor clusters when including a Lightbulb?
3.	Is this a known limitation of the Arduino wrapper (single “actuator” device), or a bug?
4.	Would this require using an Aggregator or a different pattern not yet exposed at the Arduino level?

I would be happy to test any suggested changes or provide logs if needed.

Thanks again for your support and for maintaining this library.

Best regards,
Simone

[Tamas Jozsi (silabs-bozont)]

Hello Simone Genovese (@simonegenovese),

Thank you for your report! It's definitely an odd case you encountered. Having two or more lightbulbs with the Matter library is supported and should work. I just did a quick test with Google Home / Apple Home - and indeed they work. (I used the built-in matter_lightbulb_multiple.ino example)
To answer your questions:

• Mixing and multiplying of all kinds of devices is supported - the library adds them as separate endpoints. It doesn't support adding more than one device to a single endpoint yet.
• The library takes care of everything regarding endpoints and clusters - no additional lower level actions are required by the user
• Not a limitation that we know of - we test with Home Assistant/Apple/Google/Amazon ecosystems - unfortunately not with SmartThings. I could imagine that the issue is something SmartThings specific. Could you please share what kind of SmartThings setup you use?
• The library adds an Aggregator endpoint on endpoint 2 to ensure compatibility with dynamic endpoints, but it can also be turned off

It could also help if you posted the modified sketch which is failing for you!

Thank you for the kind words, happy to be maintaining the core and supporting you!

[Simone Genovese (simonegenovese)]

Dear Tamas Jozsi (@silabs-bozont),

Thank you foro your support.
Here the file.
matter_sensor_multiple.txt

I'll try with Home Assistant and let you know.

[Simone Genovese (simonegenovese)]

Dear Tamas Jozsi (@silabs-bozont),
I tested on an Adroid device, and the only difference from iOS is that, now I can switch between one device and the other changing the Driver.

But I can't have both at same time on the Dashboard.
Any help?
Thank you
Simone