I use a lot of AirTags. One of them, located (I believed) at my son's house in Silicon Valley, only checked in to the network every once in a while. When I would go to find the physical tag, it couldn't be found on the network. But then, when I would be in Europe or somewhere, it would randomly check in to tell me the battery was low. A few months ago, I tried to find it using the "Directions" feature of Find My, only to have it lead me down the street. I thought it was hallucinating.
But today, I saw that it recently popped up on the network, so I used the directions app to track it. Again, the app led me down the street, then across the street. I used the "Play Sound" feature to make the AirTag beep. And I found it! It was half buried in leaves where it had been exposed to the elements for a year.
How did it get there? Well, the best guess is that neighborhood kids were playing with it — kids whose family moved out of the neighborhood nine months ago.