Unexpected email notices about 1Password sign-ins

I get periodic emails from hello @ 1password.com about new sign-ins. Got one a little while ago - at a time when I was doing nothing on any device. All my devices were idle or sleeping.

It's not clear what the email even means -

"Your 1Password account was just used to sign in from 1Password for Safari."

Used to sign in to what?

To the vault?
To some web site, using 1Password-supplied credentials?

I deactivated the inactive devices in My Profile, then manually deactivated 21 more that were still present (!), then signed up my iPhone and iPad using the scannable setup code.

I left 2 older entries in the profile - for my Mac, and for Safari.

Some of the ones I removed were reporting IPv6 addresses.

The one for Safari - which is accurate and reflects my actual last access at 1password.com, which I've been actively using - incorrectly reports macOS 10.15.7. I'm using 11.5.2. Did older info get stuck in the device info you have recorded, perhaps based on the OS in use when the device was last authorized?

The one for my Mac name is correct.

While typing this up I just got another email notice reporting a sign-in from 1Password for Safari - it reports an IP address in the range that Apple is assigning Private Relay IP addresses from.

Perhaps it is the change in IP address that is triggering the warning? But why is my phone or iPad signing in? I wasn't using them.

This new one was added as an authorized device.

So I now have these 5 authorized devices:

Mac name, actual IP address, macOS 11.5.2
Safari, actual IP address, macOS 10.15.7
(that's the wrong macOS version)

iPad Name, actual IP address, iOS 15 15.1.0
iPhone Name, actual IP address, iOS 15 15.1.0
Safari, private relay IP address, iOS 15.1

(cannot tell if this was Safari on iPhone or on iPad, since you seem to report the text "iOS" for both kinds of devices. But because it's reporting a private relay IP address, I know it has to be one of those and not the Mac, where I don't have the feature.

Can you shed some light on these notices?

Thanks.

1Password Version: 7.9.1
Extension Version: Not Provided
OS Version: macOS 11.5.2