@Kenny_L 

I'm having a similar issue with one of my many Kasa switches. I have 7 switches and 4 plugs. Some have been working wonderfully for years via Google home.

Recently one of the switches, an hs200 v3 on FW 1.1.5 started being "slow".

For Google home, it takes 10-15 secs to turn on. And Google home will complain that it cannot find the device.

On kasa app is a bit better, but I can still see that when opening the app, this switch is sometimes greyed out (offline) while the other switches are ok.

I suspect the switch has a weak connection (app says -43db tho) or is sleeping?

Not sure what's going on but it's terribly annoying.

One thought I had is that I recently updated the firmware on my omada esp access points. I have a 225 which was updated from v5 to v5.0.5. not sure if that's related.

@Kenny_L I've had the same issue with my HS200 switch and all three of my HS105 plugs. I have several HS103 plugs that are still working perfectly.
 

Like other people I've never had a problem until about 2-3 months ago. I'd been using the devices with Alexa flawlessly for over a year. Now all four devices only work in "local" mode in the Kasa app and it often takes several seconds for them to turn on/off. They don't work with Alexa anymore and Alexa reports the "device is unresponsive".  
 

It sounds to me like there was a backend system change at Kasa, maybe a timeout setting was changed and now it's too short, I have satellite internet with very slow upload speed (1 mbps) and high latency (600 milliseconds). My HS103's are still OK and my only Leviton smart switch is also working fine. 
 

I've reset them, updated the firmware, followed all advice on the TP-Link site except calling support (who has time for that) all to no avail. They are no longer "smart" devices. 

I discovered that my offending device has a label on the back stating it's V4, but the firmware reported on the app shows HW v3.0. I wonder if somehow the app flashed the wrong FW to the device. Or maybe v4 is the same as V3...

I also have a 103 which is showing the same behavior. It shows V2 on it's sticker but the software shows v2.1.

I wonder if somehow in the recent past weeks, there was a botched firmware pushed which is somehow causing devices to refresh less often than required?

@elmado 

All my HS103's have hardware version 2.1 and firmware version 1.1.4

My HS200 is hardware version 2.0 and firmware version 1.5.7

The HS105 is hardware version 1.0 and firmware version 1.5.6

When I request a firmware update the Kasa app says No Updates Available

One thing I've noticed when going into device info for the HS200 and HS105 is that it takes about 10 seconds for the time zone, device time and wifi fields to populate. Those fields on all of my other devices are populated as soon as I open device info.

The wifi signal is strong on all devices e.g. -32 dBm. I have all three different products in the same room within a few feet of each other and only the HS103 works consistently.
 

@pointingfinger 

Yep I have the same behavior. My bad HS103 is the same hardware version and firmware version as your.

I have other HS103's that are all v1.0 and they work fine. So perhaps it's firmware/version dependant.

@Kenny_L 
I saw the same problem on my side, but I was alwasy able to resolve it by follow a plan:
1. Clean app cache on the phone, reboot your phone
2. it takes a few days for new smart devices to start performing
3. Reboot your switch (right button press on switch for 5 sec)
4. Check if you have too many wifi devices in particular access point, some weak/cheap AP behave weirdly if you have more than 40 devices connected. For pro AP 100-300 devices is not an issue.
5. Check if there is any wifi clients conneced to your AP with signal -78db and lower - these clients could cause wifi network instability, even if your other device has a good signal rate
6. Check for microwave nearbuy or bluetooth device or even Zigbee and Thread devices - they all can cause 2.4Ghz network instability as well.
7. Check for quality of electric connections on switch, in controlled by switch chandelier, try to switch light bulbs (could cause interference)
8. Check for wifi noise level close to the switch - your neighbour with his devices could be your issue as well.
9. Check your internet firewall if it is blocking any connections
10. Assign static IP to your switch.
..... and so on.

Good luck, I hope you will find your solution. 

@Yokushka 

I have good news - I fixed my problem.

The bad news - I had to replace the switch with a new one.

TP-Link support was willing to replace my switch under warranty, but shipping it back costed more than a replacement...such is life.

Anyway, hope this helps to confirm that it truely is specific to the switch.

I still suspect an incorrectly updated firmware issue, but I have no way to prove this...I see the same problem on two different firmware versions of some v1.0 HS103s.