y0din

ignore my previous comment which I deleted and make sure your hue network and firmwares are fully updated. some devices where/are still exploitable today if the update is not applied.

https://blog.checkpoint.com/security/the-dark-side-of-smart-lighting-check-point-research-shows-how-business-and-home-networks-can-be-hacked-from-a-lightbulb/?theme=dark

deleted by creator

my hue devices support Bluetooth and Zigbee devices to allow for management through an app or a hue hub.

even if you do not use it, it will be available and active, and it explains your issue. I have had my neighbors lightbulbs added to my Zigbee network before I kicked them out, and I will imagine his cloud service saying about the same as you experienced.

but, I will not try to argue this any further, I just offered a probable reason, as that was what you asked for.

good luck in your investigation 🙂

that is probably someone who is connecting / pairing your Zigbee bulbs to their network/mesh.

it has nothing to do with the cloud service.

if you are not using Zigbee yourself, they auto join open Zigbee networks after reset or when they are not connected to a Zigbee network, so if the other person is adding a new device he or she owns, the bulbs will also join his network in that process.

unsure if you can switch Zigbee off in the app or not as I have never used the app, so you would have to figure out how to do that yourself or make them join a Zigbee network you own.

hope this helps and hope you get it sorted.

(edit, added line about cloud service)