Oh poor mite! And how stressful for you too! Yes, agree on getting a vet check! Also distance is your friend. Start at a distance he doesn't react and give lots of treats and praise and slowly work closer. If he reacts, move back again. It's an ongoing process but hopefully he responds quickly. But definitely the vet check first! X
I would find a behaviourist, and get a full vet check up. Think you will need some support with this x
Definately vet for a check up, and then maybe if he doesn’t already try teaching the ‘leave it’ command, start at a distance so he’s not too close and then work your way forward x
He might just be overthreshold due to the kennels and need a break from your usual walks. We gave our dog a 'holiday' from usual street walks and drove him to more remote places for walks or even just a field to sniff around. It let him decompress and we eventually got back to street walks again. It's just trigger stacking when the keep reacting to everything, they need a wee reset. Could be a few days or weeks they need, we gave our dog a few months of remote walks because he was really struggling
If it's a sudden change in behaviour it's always worth a vet check to make sure there's nothing medical triggering the oversensitivity. The vet can also advise on dog behaviourists - depending on the insurance you may even have behaviourist covered.