Okay, so, the thing with this is, the whole reason that the event wasn't working is that leashes were never actually getting deleted when they expired. They just stopped showing up.

There is supposed to be an event when your leash expires, but the way it was being given was in a really awkward place (like you'd have to actually go to the pet's leash page in order for it to delete/give you the event, it was not an automatic thing, which is completely useless to be honest). Now that the event is being given/expired leashes are being deleted automatically, it's also giving events for long-expired but never deleted leashes.

So it's actually not a bug. It's just that, despite being expired, those leashes were still in the system. But now they're not anymore!