@BrianMal 

I'm also having the same issue with the periodic/semi random white blinking LED ring on the S515 setup as a 3 way. I have it showing in HomeKit and it the light reports itself on and off multiple times every minute even though the actual lights to load are not on and off.

My theory right now is that my other "dumb" 3-way switch in the circuit is an old backlit illuminated rocker (likely using AC to a small filament) that pulls enough watts to light the rocker switch. That maybe triggering the smart switch to think that the lights are on, and then off.

Need to get a non illuminated dumb three way to test this out further.

  @TechBro 

Since I first reported several issues to tp-link in January, I have received 4 weekly firmware updates, each one fixing a part of the issue. I received the last one this morning that fixed the switch not coming back online after a firmware upgrade. However, I am not sure if they have released any of these for general distribution as others have reported they don't see the versions I am getting. All versions have been 1.0.4 but today's is 1.0.4 Build 250214 Rel 120349. I think most, if not all, your problems should go away once they release the final version.

Brian

  @TechBro 

Forgot to mention...

From what i have figured out, the switch intelligently determines whether the light is on or off by which line draws power, hence why the other switch has to be 'dumb'. Apparently, the threshold for this is around 1/2 watt. That bulb in your other switch might cause an issue so might be worth replacing or bypassing it to test.

Brian 

  @BrianMal 

Nope, I was wrong. I the blinking LED problem is back. *sigh* I still need the newer firmware I guess. 

NEVERMIND what follows: In the course of getting images of the labels on my S515 so I could provide it to tech support (at their request) I found that the NUETRAL WIRE WAS VERY LOOSE. I did not have a good connection with my wire nut. After I redid the wire nut and put everything back together, my blinking LED problem was gone.

@BrianMal 

It's fixed! The new firmware was pushed to my switches and the problem is gone. I can now use my S515 3-way light switch in a smart way. When I turn on my kitchen ceiling light via the S515 switch, I have two smart electrical outlets also turn on for my under cabinet lights. It works great (a little lag sometimes but I don't care about that). My firmware is 1.0.5 Build 250210 Rel. 142737. Hurray!