I've seen this happen a couple times, and I'm not sure if it's a WilderCraft issue or not.

1: I had a tamed cat in Willow for several weeks and it became a stray again while in the house. It was almost surely the same cat unless someone took my original cat somehow. It did not have a nametag.

2: A tamed dog in my town on Maple was no longer tamed and was very very low health. It was sitting down still, and I was confused so I hit it thinking it would fix it somehow. It did not and it died to my thorns armor.

3: Another dog with the same owner as the dog above was no longer tamed, very low health, and sitting down. It was not nametagged, and I found another dog inside their house with the same issue but this one was nametagged.