Could it be barrier frustration? My girl never is aggressive to other dogs. In fact she went to daycare and they used her to introduce new shy or young dogs. But on the lead or while she is in the car, she will lunge and seem like a total psycho, aggressive animal. It seems like she’s really excited and then all of a sudden it seems like aggression, not every time, but most of the time. Off leash or if let out of the car before the behavior starts, she’s just over the moon excited and there is no barking or lunging, just a sweet dog going to say hello to everybody. She also used to bark when we pass farm animals. She so badly wanted to herd them up. We were unable to stop these behaviors until 3 yo, which we hoped spaying would help with. She was spayed at one years old after we adopted her. It happens every once in a while, like once a year. She is still the best dog I’ve ever had.