@Wayne-TP 

Hello, 

Like I previously said. 

All 3 dimmer (in fact 4, I forgot I had a forth one and it did the same problem tonight) are connected to different fixture on different circuit. All light circuit are dedicated. 

They are not overloaded, it's only led light bulb. You need a lot of these to overload a 120v 12a switch. And unless they have a lower rated voltage than the hs220, why is the issue not present with the hs220 but is with the Ks220m? 

1 of them is connected to a single light bulb (the one I forgot to count that stopped working tonight). One single bulb that is dimmer compatible. I replaced both the fixture and lightbulb about a month ago. 

Another one is connected to an led stripe bought at Costco that is non dimmable. Thus, in setting, the lower and max value are both 100%. It's a temporary lighting in a room I'm renovating that will have dimmable fixture. This is where I first saw the difference between hs220 and Ks220m turn on/off behavior. Where the hs220, when fade on/off is disable, properly cut the power instead of lowering while the Ks220m, even with fade off still do a curve shutdown that my fixture hate. 

In my kitchen, it's a 5 bulb fixture that's been installed for 3 decades. Was working fine with my wemo dimmer, was working fine with the tplink dimmer but since I've installed the Ks220m dimmer, I get that random bug. I rma this one and the new one started behaving the same. 

The other one is in my bathroom. Again non dimmable light so 100% setting. On next renovation, the fixture will change. Here it's 3 led light bulb. 

So I'm far from overloading any of these. 

I think it's due to too much WiFi traffic. I have over 60 WiFi device and will reach 100 easily by the end of my renovation. I have 2 unifi u6-pro so I know I have the WiFi capacity. 

But I remember something. About 6 months ago, I started having weird problem with tplink devices. They would not connect anymore to my WiFi. At this time, I had an Asus router that was broadcasting its own WiFi ssid just for iot devices. When I restarted the router (it was more of a switch + WiFi ap cause I wasn't using any of the router feature), I saw all my device starting to connect, get connected than half would disconnect and be unreachable. I had similar problem with my switches at that time. This is when I decided to create an ssid on my unifi network and have them connect to it. Until now, I though it had fixed the issue I have with the dimmer but it has since came back often. I've looked at my WiFi and I cannot reproduce the issue I had with my Asus so I know my WiFi is stable. 

Right now, I still have one that isn't working if debugging is needed. 

  @Wayne-TP Hello, no the issue is only that the light doesn't turn on. It's like if the relay doesn't get the turn on signal. As for how much time the control last once it's restart, it's random, there's no fixed time.