@board4mic May I ask have you tried on any dimmable smart switch to realize a 4-way switch? 

  @PatchyFog thanks, got it figured out. Took a multimeter and a few hours of trial and error. Ended up being the 4 way paddle switch from Amazon. The switch pattern is not same sides and the crisscross. It is same sides and then same ends. So I had to put the travelers diagonal to each other. It was an enerlites paddle switch.

  @ejayb A 4-way switch won't function at the end of the circuit -- and the Kasa 3-way will suck power from any active line, so it is hard to disrupt their juice. You're probably going to have trace wires with the juice off; but another approach would be to put 1 Kasa in at a time and see how they behave. You might find my video helpful: https://youtu.be/kMT7KUVTELo

  @Chicago_SH hello. Recently installed according to drawing. Left the 4-way switch alone and only added TP-Link 3-way switches on the other two locations. Problem is that when I flip the 4-way switch it turns off the power to one of the TP-Link switches. So I'm guessing the 4-way switch is on the end of the circuit not in the middle. Can anyone confirm if that is probably the case or something else happening?

  @Augustlion This thread is long enough that it might be time to plug my deep-dive video on this topic here again. It may help you. https://youtu.be/kMT7KUVTELo

  @xRkYqUz Yes, that's what I'm currently trying to install.  Believe me, the struggle is real!

I need to try some continuity tests, but I think this is my setup.  Between the positioning of the lights, and a 3-way at a dead end, it's driving me crazy.  If anyone has a solution to this I'd really appreciate it.

My instinct is to try the HS210's instead.

  @Ant._. I have 1 3 way replaced with a smart switch and it is working on the app. The other 3 way at the other end does not have a neutral wire. If I connect a second smart switch without the neutral connected, will it be able to tell if the light is on or off?

@Carl yes, this is exactly how I'm setting my switch configuration, with one tp-link 3 way switch at the end with the neutral wires, one regular 4 way, and one regular 3 way. I believe this will function fine.