Hey everyone

So I have a 1.5 Great Pyrenees and since I got him he has been coming to work with me. So he has constantly been around people and other dogs since he was 8 weeks old. He has gone to the dog parks so many times and no problems. Before he was neutered, he would get obsessed with a dog and if another dog came up he would bark aggressively. Once I got him neutered that stoped. But recently in the past couple of months, he will randomly bark aggressively toward dogs. For example, thereís another dog across the street and he will bark at it. Most of the time he is fine and wants to play bc he does love other dogs but itís super random dogs he gets that way with. Another time will be at a restaurant or something where he has been so many times. And now if another dog comes in he will bark meanly. The most recent time was at the dog park. He was fine and as we were leaving another dog was walking in. He sniffed it and then I pulled him to leave and he snapped at the other dog. He will never bite just aggressively bark and it scares people. Anyways I donít know what to do or how to stop it. I get on to him after he does it. HELP!!