After I updated to HA 2026.9 I noticed that my HA cloud connection wasn’t working anymore.
In the HA UI it showed something like “preparing”. Nabu Casa showed offline.
Signing out and then trying to sign back in returns Authentication timed out..
Nothing relevant seems to get logged.
Updating to 2026.9.1 didn’t help.
/edit: Internet connectivity isn’t the issue. My connection works normally and other cloud based integrations also work fine.
I’m having the same problem. I wonder if it has something to do with AdGuard Home or PiHole blocking something that Nabu Casa is using that’s new or newly blocked
I found a “sulution”. Disabling IPv6 Router Advertisements on my router and a restart of HA caused the login to work.
My v6 connectivity looks alright, but it seems there’s something wrong at some point and the v4 fallback doesn’t work right.
So the problem is almost certainly that **Home Assistant 2026.9.x is trying to use the broken IPv6 path for the Nabu Casa Cloud connection and isn’t falling back properly to IPv4.
You don’t need to kill IPv6 on your entire network. Just on your HA instance.
I had a broken default route on my RPi HAOS.
ha network update end0 --ipv6-method disabled
kills IPv6 on the Pi while leaving the rest of the network alone.
“Disabling IPv6 Router Advertisements”(on Unifi) didn’t work here.
I downgraded back to 2026.08.3 and even then I could not login again from within HA.
The fix to get it online again (after the downgrading) was to logon to the nabucasa website → account settings → button “Log out” in section “Log out from all devices”.
This might also be the solution when you’re on 2026.09.x, but I haven’t upgraded again to try this.
I was also able to (temporarily) fix this by disabling IPv6 in the Settings > System > Network tab after connecting with the local IP address.
This can break Matter connections, however. Hopefully a fix can be rolled out quickly.
Is this fixed yet? I have been having lots of issues connecting and just opened a ticket. I’m on 2026.09.03 I think - decided to log out of nabu this AM and haven’t been able to get back in due to connection time outs since then…
As far as I know, this isn’t a bug, but just that HA from now on uses ipv6 to go to the internet if an ipv6 address is available and no longer falls back ipv4 if the ipv6 address isn’t working.
Which means that, if ipv6 has been set up, it needs to work correctly. If you don’t need it, you can turn it off, but if you do (for matter/thread for example) then you need to have it active and set it up correctly.
I’ve had issues too and had to switch it off from my WAN connections and only use ipv6 locally to get the issue fixed(because I’m using Matter over Thread), because one of my providers didn’t support ipv6 correctly.
This is the official page about this
I had this same problem earlier this year and disabling ipv6 on my HAOS did in fact fix HA cloud for me. But once working again, you can simply re-enable IPV6 on your HAOS again.
FWIW, I got disconnected from the Nabu Casa cloud, then start experiencing this issue too, except, I couldn’t get it fixed. I tried multiple reboots with/without IPv6, I tried logging out of all sessions on the Nabu Casa website. I tried removing the matter server altogether and even downgrading to 2026.8 but nothing seems to work.
Edit: I tried to go through the whole reboot flow one more time before giving up, this time it worked.
I logged out of all accounts on Nabu Casa, then cleared all cloud data in HA, rebooted the Pi, waited some 10 mins and tried to sign in from HA. That worked. 
Posting after figuring out my issue after a lot of back and forth led to realizing this was (for me) a Verizon FIOS plus router problem. I use a Firewalla and they had figured out that Verizon FIOS rotates IPv6 addresses every hour or so which leads to a lot of stale addresses. I had to turn off IA_NA. Hope that helps.