Make sure that either the 2.4 gigahertz band or the 5 gigahertz band is enabled on your router. The DHCP function must be activated on the router. Authentication via MAC addresses must be deactivated.
All Wi-Fi-based devices with HomeKit support require the Bonjour protocol (Multicast) to work. Make sure that Bonjour and Multicast are enabled on the Wi-Fi router and additional access points.
Network tools such as "Storm Control" and others, allow multicast to be restricted and therefore Bonjour. Disable this setting.
So-called Powerline/PowerLAN adapters also restrict Bonjour or do not allow it. These access points are not suitable for the use of HomeKit-based Wi-Fi devices.