Keep getting 'Accessory Already Added' error, when trying to add Smart AC to HomeKit

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The Smart AC Control is not in HomeKit anymore. I have removed it also from Tado Home and reset it to factor setting several times, but to no avail. Even removed and created a new home in HomeKit, but that didn't help either. Also, changed my Wi-Fi to 2.4GHz as instructed. Nothing seems to help. What's up?