Well spotted, that looks like the source of the problem.
PSA: If you own a Hubitat hub you can use the TP-Link app to unbind the TP-Link devices from the cloud so youāll never have to worry about them updating. The downside is that you can no longer use the app. (not an issue at all for me)
I have the same problem. In the UK and bought a pair of HS100 to use for my Christmas lights this year. Upon installation of the plug using the Kasa app it performed a firmware update to 1.1.0. I have been wondering why the new plugs were not being discovered by home assistant (my other 6 work fine). Looks like it is this firmware level which broke it.
Does anyone know which DNS names to block so all my other plugs cannot get the update?
I just checked my other plugs and it appears that the HS110 devices which are on firmware 1.2.5 and some on 1.2.6 I am still control via HA fine. (Hardware version 1.0)
Any of the HS100 which are on firmware version 1.1.0 are not discovered and not able to be controlled from in HA. (Hardware version 4.1)
Iām using the german version of HS110
It shows HW 2.0 and Firmware 1.5.6
Not sure when the last update was but it is still available in HA
as soon I get an firmware update I will not install it
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Copied from my post at Tp-link HS100 H/W 4.1
I have a few HS100 plugs that were purchased at different times, so I happened to end up with different H/W versions.
H/W V1 Firmware 1.2.6 - Works
H/W V2.1 Firmware 1.5.10 - Works
H/W v4.1 Firmware 1.10.0 - Communication Error
KP303 - HW 1.0 Firmware 1.0.4 Also works.
So oddly whilst the older H/W versions also got a new firmware they still seem controllable by Homeassistant
Annoyingly the 2 I use most often ar the HW 4.1 ones 
Iām in the same boat, one of my plugs is on hardware version 4.1 and firmware version 1.1.0 and I can no longer see the device in HA. Blocked the other plugs in my network from connecting to the internet so hopefully those will continue to work in HA. This is very annoying.
How did you do that? Iāll have to do the same for the hs100 I still have untouched in a box. Ta!
I blocked mine as well from the accessing the internet.
I blocked it in my router
Gave them a static ip address and blocked that in my router.
I have one new in the box too but donāt want to link it to my account in case it applys a firmware update. I guess it needs internet access to register with your account or can it register without internet access?
I donāt think I can do that on my bt hub 
@Jamezz98, I honestly canāt remember if you need the app/account to set it up or not. My gut feeling says yes though. 
I replaced my bt home hub ages ago so canāt check, but https://community.bt.com/t5/Home-setup-Wi-Fi-network/Restrict-internet-access-for-a-device/td-p/1989323 suggests itās not easily doable.
Yeah, I saw that and all I thought was āfine, give me the non easy way then!!ā The options further down werenāt helpful either. Oh well. Guess Iāll continue to bug tp-link customer service instead.
I believe (because it worked while I was diagnosing my original problem and did a factory reset of my plug) that you can set up a new device with the Kasa app while the device is unable to reach the internet, so long as the phone running the app can sign in as normal.
The BT hub is crap for configurability, but you might be able to temporarily block the plug using the parental controls? As I recall mine wouldnāt let me block any device permanently though. Which is why I now own a better router.
No response from TP link to my enquiry yet, and my hopefully-esphome-compatible plugs are due to arrive from Amazon today.
The parental controls block local access as well, it complete blocks Wi-fi connections.
Tp-link answered me on Twitter, but that was the useless āit was a necessary improvement for safety, and you should only use the KASA app anyway so stuff youā type of reply. I asked them to consider at least an opt-in for local access. No response yet.
I also contacted TP-Link asking if itās possible to downgrade to the older firmware, Iām not sure if itās by design that itās now blocked from working or a bug.
I would have thought if it was by design the new firmware for the older HW revisions would have blocked access as well and it doesnāt seem to have done so.
Honestly Iām not really expecting much from TP-Link, but I figured it was worth a try.
I think itās by design, because Which?, the British consumer advice group, complained about lack of security. See my screenshot in reply 12 or something, taken from the Which? article. Thanks Which?! 
I just received a reply from TP-Link andā¦ itās an out of office notification! 
Possibly but I think itās a bit odd that the earlier HW revisions also got a firmware update yet still work with Homeassistant