@Nogard13 

I want to say its a wiring issue because has happened on two separate products.  Looking at the HS210 you have 3 screws as you know.  2-Brass and 1-black.  Plus you have the ground wire and neutral wires coming out of the back of the switch.  The line or load wire should connect to the black screw, while the two traveler wires should connect to the brass screws.  Additionally if only using one HS210 in a run you want to make sure the manual switch is on the load side and not the live/line side.  This is because the HS210 needs a constant supply of power to run the wireless module and allow it to be controlled manually and through the App or a voice assistant.  

It sounds like you already know what you are doing, but when it comes to electrical concerns its always better to check then assume. 

@Carl 

Hi Carl,

Yes, the hot is connected to the black screw (always hot unless breaker is off), with two travelers connected to the brass screws on top.  The manual switch also has a hot line that is always hot unless the breaker is off.  I don't know which one is the first as I did not wire the house, but I guess I could try swapping the two switches (manual and Kasa).

Interestingly, I switched the two traveler wires around (left to right) on the Kasa and now the flickering/clicking is when the light is turned off from the toggle switch, but in the opposite position.  It used to flicker/click when I turned the lights off going downward. Now it does it when I turn the lights off going upward.  If the toggle switch is up, and I turn the lights on with the Kasa, then off with the toggle switch, it works just fine.  However, if the switch is down, the lights are turned on with Kasa, and I toggle it up, then it flickers and clicks.

@Nogard13 

I do know that the travellers have to match on the switches, so for instance say you have a Red and Black traveller wires and have the red wire as traveller 1 then it should also be traveller 1 on the other siwtch and vise versa.  

Typically what you see when the manual switch is on the Line side and the Kasa on the Load side is that Kasa will have no power and show up grayed out in the Kasa app.  It will be unaccessable unit the manual switch is turned on.  

You mentioned that you have switched out the Kasa Switch.  Were these switches in the same pack or seperate packs?    

@Carl 

Hi Carl,

The switches are from separate packs.  One was purchased from Amazon, the other from Home Depot (locally).  Both exhibit the same behavior.  Additionally, I checked the old switch (the first one) again, and it has the exact same behavior.  I had Red/Black as Traveler 1/2, respectively originally.  I switched them to be Black/Red (1/2) and the same issue persists, only when the toggle switch is in the opposite position.

Both of the Kasa switches are powered and show in the app, regardless of the toggle position.  This tells me that the Kasa switch is always powered, either with Line or Load.  I'm going to try to make some time today to swap the toggle and Kasa switches to see if the issue persists.  The only thing I can think of that could be the issue is that the toggle switch has a dimmer on it, but I've made sure that the dimmer is always on max.

@Nogard13 

I may need to send this to the Engineering team for anyalsis.  I personally am using a HS210 in the same exact manner but have not experianced this issue.  The only other thing i could suggest is if possible replace the other (manual) switch with an HS210, so that both switches are HS210s.  If you could, at least for testing purposes and see if this situation is still happening.  This would also give me addtional information for the engineering team to look at.  One other question just to possibly rule it out.  What is the amperage of the circut these light switches are on?    

@Carl 

I solved the "issue" but still don't know what caused it.  I swapped the toggle and HS210 and the issue disappeared.  Now I can operate both switches without the lights flickering and the HS210 clicking.  The only thing I can think of that is different is that I now have the HS210 on either the Line or still on a Load, but upstream from the toggle switch.  Why that would matter, I do not know, but I tested both traverlers for continuity to make sure I knew which was which (even though it's red/black) and had them connected to the same positions as prior to swapping the HS210 and the toggle switch.

I honestly don't GAF which position has the toggle and which has the Kasa, but I just find it weird that the behavior stops simply because the HS210 is upstream from the toggle.

@Nogard13 

If the HS210 was on the load the concern you would see if that if the manual switch was switch to its "Off" position the power would be cut off to the HS210.  This is why the HS210 should be on the Line or live side.  It needs to get a constant flow of power to power its wifi module.  When on the load side this isn't possible.  Normal operation can still happen if the manual switch is on the Line but it would need to remain in its "On" position.  What you were explaining didn't make sense as it didn't appear to be a power concern @Solla-topee  what do you think about this one?  What would cause the concern in this thread?

@Carl 

Normally, when a switch is connected/dependent on another for power, it's when the first switch feeds the second with a load wire.  That's now how this is wired.  The toggle switch and the HS210 both have power being fed to them in the box from live wires that also power other switches in the same box (both are 2 gang).  Because both switches in the box share one power wire (which comes in on a 14/3 wire and then wire-nutted to two wires that feed each switch), I didn't think it mattered what side each switch was on. That is why the HS210 still has power even when the toggle switch is in the off position.  The box that currently has the Kasa also has a 3 way switch to control the light on the stairs down to the basement while the box with the toggle switch on it currently has a 3 way switch that controls the lights in the hallway between the Rec Room (what the Kasa controls) and the bedroom.

Like I said, both boxes have a wire that has constant power and the Kasa always showed in the app and was operational regardless of the position of the toggle switch. 

@Nogard13 

Hmm.  Okay I will admit up front, not an electrician and i know very little about it.  My knowledge of a 3-way box is as follows:  1 box (main) contains:  2 - traveler wires 1- line(live) wire 1- neutral and possibly a ground.  The 2nd box contains:  2- traveler wires 1- load 1- neutral and possibly a ground.  If I read what you were saying correctly your boxes were multi gang. Does that mean when you first had it set up you put a powered wire on both switches?  If that is the case it is very likely that was causes the concern.  I just wanted to confrim before i sent it up.  

@Carl 

Here is how I think it's set up:

Power comes from the circuit breaker into the wall outlet that is at the bottom of the stairs (since it's the closest to the circuit panel).  From there, power moves in series to each gang box, then connects to everything in it in parallel.  So while power goes to the first outlet, it then goes out from the outlet into the second gang box, which has 2 3-way switches.  From here, there are 4 hot wires that are joined under a wire nut, one goes to each switch, one comes from the first outlet, and one goes to the next gang box, which is an outlet.  It moves down the line, outlet by outlet, until it reaches the other 2 gang box where the 2 3-way switches are, then one more outlet, then one single gang 3 way switch where that run terminates.

That's what I think is happening as I did not wire the basement. :)