Any of your toddlers potty trained? How is it going?

My boy was gently potty trained starting in the summer and then gradually going into his bday when I decided to take nappy off entirely and gave it a go. He done amazing, no accidents home, about, nursery nor even on holiday we went on Christmas. But after that it’s an accident after another. He has just stopped telling us he needs a wee or a poo and just does it silently in the corner (in pants) and then cries out? He use to go toilet himself with no prompting. Any ideas what the hell is going on?