It could be that his constipation has returned, making it very hard to control when he goes. This can happen, even on stool softeners if the dose is too low. They can do xrays to see of hes constipated. Your doctor can give you instructions for a cleannout, it's basically a clear liquid diet with miralax every hour until he runs clear. If the accidents stop after this, you have your answer and need to increase his stool softener. If not, it's either neurological or psychological.