I had the thought too, but there is no way anyone else could have gotten physical control over this and shouldn't I see that AirTag when I scan for things in my surrounding as an anti-tracking protection?
I've had similar issues -- consider it a bug -- and unpair and re-pair with your phone, and likely the issue will go away.
i’ve had this happen due to going from beta builds to stable builds or vice versa. not super clear exactly which of those triggered it, or whether it was just a beta build bug, but the 5x reboot always fixes it