HomeKit Stops working with Meross, Kasa and other IoT devices

I use HomeKit for all of the automation. It works great with integrating all devices into one ecosystem. A few months ago, many of my Meross and Kasa devices, along with a few other manufacturers, stopped working with HomeKit. This happened after the iOS 17.3 update. I have researched this over and over until I finally figured out what the problem was last week.

I have read several other posts on the internet saying this also happened to others. My first thought was that these devices needed to have their firmware updated. I made sure that was done and no success. BTW, when setting up new devices for HomeKit, you should make sure these devices are also setup in the app published by the manufacturer. This will ensure you can update the firmware. I got frustrated and just lived with the issue for a few more months hoping that either iOS updates or firmware updates would resolve the issue. It did not get fixed. 

I then started researching the possible cause as being the router. I have a TP-Link Deco router. It is a fantastic router to own as it is feature rich while also providing cloud features. In researching one device, I found through Wireshark that the device was not able to communicate with HomeKit through my Apple TV that was functioning as the hub. The device was trying to talk to my Apple TV, but was blocked. It was then that I realized it was the router causing the issue. 

The first thing I did was make sure the devices that can only connect at 2.4 GHz were specified in the settings as shown here. 

This did not fix the issue, but it made sure the device would connect through 2.4 GHz. The next thing I did was to move it to the main network from the IoT network. The IoT network was configured only for 2.4 GHz. This still did not fix the issue, but it was well on its way. The main network is configured to accept both 2.4 GHz and 5 GHz connections. I have seen posts while researching this asking for TP-Link to please add the ability to split the network to advertise separate SSIDs for 2.4 GHz and 5 GHz connections. This is not needed when you define the above settings. 

The last thing I did was to disable device isolation as shown below. The issue was fixed. Not all devices had to have device isolation unchecked. My Meross devices still work with device isolation enabled. Kasa devices need it disabled. The Mysa thermostat needed it disabled. 

So to summarize, you will need the devices all on the same SSID. Devices requiring 2.4 GHz will need to be specifically defined as shown above. Device Isolation may need to be disabled depending on the manufacturer. The Apple devices that function as a hub can be on either 2.4 GHz or 5 GHz while connected to the Deco main SSID. It will be able to communicate to the 2.4 GHz devices with no problems. The hubs must not be isolated.