Unlock with Watch showing wrong series and doesn't work

On my Mac Mini running Mac OS 12.6 Monterey, with a Series 8 Watch running WatchOS 9.0.2, unlocking with Watch won't work.

In System Preferences > Security & Privacy, I see my old Series 5 Watch and a Series 6 Watch I've never owned and nobody else in the family has had one either. The Series 8 doesn't show up and unlock with Watch doesn't work. Weirdly, if I select the Series 6 Watch it enables and I don't get a "couldn't communicate with Apple Watch" error.

The Series 8 Watch is correctly showing up as a linked device on iCloud.

Any ideas, is this a bug?