I just started seeing this today - it’s appearing on the 3 switches I have that are Matter switches,
Reporting authentication issues too since update. Prior to update, I could “re-authenticate” all my light switches when never TP-Link asked for it. Now, none of my KS225 will work. Getting “Unknown Error”. Other devices work fine (KS205 and KL125).
KS225 running firmware 1.1.0.
Tried HAOS reboot/restart, and tried factory reset on light switches.
EDIT: Just installed newest update (HA 2024.7.1) and the issue was resolved for me.
Worked on this yesterday with HASS on discord. Can attest it’s been resolved in newest update.
SPECIAL NOTE:
username (email) is CaSe SensiTIVE
use kasa app > goto “Me” section to view your email address.
my email had Gmail.com with a capital “G”
2 Likes
Having the same problem with one of the EP25’s, and even though it says authentication successful, it still shows as an error in HA.
THANK YOU! I kept trying my username that is shown on the top of the screen because my email didnt work. I must have typed the wrong password the first time.
I have the same issue since yesterday with my P115 sockets. Also have problems with my TP camera integration. I feel sad 
Morning
Im having the same issue suddenly with the intergration. I removed it and re set it all up, power cycled the P115 plugs and it worked for like an hour.
I now just see this in he intergration which isnt helpful
ANy ideas whats going on? Im hoping its a bigger issue than just me as ive not changed anything
Thanks
2 Likes
I’m seeing something similar. My four P110 plugs are visible and controllable in the TP-LINK app, and they work fine through the Amazon Alexa “Skill”.
However, Home Assistant gives me the same “Failed to set up” message that you see.
I tried removing one of my plugs. It gets re-discovered, but entering the (correct) credentials for TP-LINK results in a “unknown error”
I turned off 2FA on my TP-LINK account in case that was something to do with it, but it still fails at that point.
Steve
Just to be sure I was using the correct credentials, I logged out of the phone app and logged back in.
I should add…
Unlike your case, I have not (knowingly) updated or changed anything just before I started noticing problems.
I have some gauges that show power consumption on my four plugs and yesterday they started to intermittently show error messages before, fairly quickly, settling down to a permanent error status.
My TP-link P110 stopped working 10 hours ago.
Firstly I experienced device temporary ‘unavailable’ in 50% cases and this lasted 2 days.
Tried reset integration, logging out, logging in without success (credentials are OK).
Now it’s gone totally
I had the same issue, tried everything mentioned in the thread.
Then I went to the Kasa app and saw firmware updates were available for all of the plugs/switches I have.
Installed the updates (two devices failed to install for some reason), restarted HA, and reauthenticated the two devices that I got the notification for.
The error messages went away and the plugs are back in business, although some sensors are unavailable (e.g. overheating).
Update: I’m pretty sure this has to do with the firmware update, the two devices that failed to update the firmware are giving me the authentication error again. Everything else works ok.
Hiya
I cant evenget them to connect in the Kasa app.
im not having much luck at all
I am kind of reliefed. Got crazy not being able to solve the issue but it does not seem to be uniqe. All my TAPO 110’s fail to authenticate giving me unknown error message.
I’ve found a working solution (for me at least) at TP-Link P100 goes offline then refuses authentication · Issue #121953 · home-assistant/core · GitHub
Tapo App → Device → LED state : Change from Auto to Off and back to Auto.
Then unplug the plug and replug in. Then it is available in HA again (needed to reload configuration).
2 Likes
Ive noticed they have included some TP link kasa python updates in the HA that I have just loaded.
I have no idea what that evens means or even if thats the issue but lets see if that fixes it
pretty sure changing the LED status is optional. unplugging it is the critical part in fixing the issue
I came in today and was having this problem with my KP125M. NFC automation didnt work and I realized it was asking me to re-auth and I entered my account into but it wouldnt authenticate. I installed the latest HA update and immediately fixed the issue. 
Thank you for this.
I tried this, and it WORKED.
Who would have thought that the email address was case sensitive!
Thanks again