Why would a trained 10 months old puppy start having accidents after being housebroken for almost 8 months?

Your puppy could have a bladder infection. This would cause the puppy to feel the need to pee suddenly, not giving it enough time to get outside. You can take your dog to the very to get medicine to cure the infection. Also check your dogs food to see the amount of ash, if there is a lot of ash, it could cause the dog to need to go to the bathroom often.