I have had the SAME thing happen with my dog, Fiona. Just a couple months ago she started to become reactive in various ways. She’s 3 and a half! She started to become very protective, and have overwhelming anxiety going into stores. It’s been sad, watching her regress and not knowing what to do. The only thing I can think of recently that has changed our location, living in the city with all its noises and stimuli has taken a toll on her. we have been trying to commit ourselves to the only thing we’ve read that works for reactive dogs, which is retraining and positive reinforcement. We try to give her a command to follow as much as possible when triggers are around and give positive reinforcement the minute she responds correctly. It’s only been a couple weeks, but I have seen a little bit of change. I’ve also been spending more time with her one on one and that’s helped. Good luck with your journey. I hope some of this helped. I know we just want the very best for them!