The short story is that I just installed an HS220. For a while, it looked like it wouldn't dim, but it would turn on and off. Today, I discovered that if other appliances are turned on (they're on what I thought was a separate circuit), it will dim, but there is intense flickering at every level but 100%.
The longer story — I have a basement room with two fluorescent light fixtures (4 tubes each). There are two 3-way switches on either side of the room. I replaced the 4 tubes in each fixture with 2 Toggled dimmable LED tubes. These wire direct to the AC line. That worked great, as expected. Next, I eliminated one of the 3-way switches (I know that the HS220 is *not* compatible with 3-way). I can get into the details of the wiring changes if that would be helpful, but 120V was now going direct to the other switch, now effectively a single-pole switch. After this, I hooked up the HS220 to replace the other switch. This switch is in a two-gang box, and the other switch is on a different circuit (let's call it Circuit B). I had been certain that I was getting line/load/neutral for the HS220 all from the original Circuit A.
I ran through the full setup on the Kasa app. Adjusted dimming values. However, the switch wouldn't dim the lights. To test, I swapped the HS220 with a Lutron Skylark dimmer I have in another room which also uses Toggled tubes and already works great. With both devices swapped and wired up, they worked great, completely as expected. I swapped back to the desired configuration being sure to use the exact same wiring. A little bit of internet searching suggested I should check to see if the two light fixtures are wired in series or parallel (I gather that parallel is required).
However, today I went to watch TV. The TV and receiver are both on Circuit B. As soon as they turned on, the lights connected to the HS220 (which is on Circuit A) flickered briefly. Huh. I tried dimming, and sure enough they actually dimmed. Except anything below 100% resulted in some pretty intense flickering from the lights. When I turned off the TV/receiver, the lights went back to full power. I'll also add that I can take the dimmer down to 1% and the lights are still at full power.
I don't know what voodoo is going on in my basement or where wires are crossed (possibly literally!). Does anyone here have advice for how to proceed? Thanks!