M.S.
I have to agree that something is going on. What did they change at school? what isn't working? If my child was told to write sentences I would be very angry. Why should something so necessary for life be a punishment?
I would agree that something needs to be changed in his classroom, like the rewards system. The screen time he gets at home may be the time he settles and centers and to take more of that away might be hard on him.
Kids with autism usually have some sensory issues going on as well, and movement is one of the most important things for them. Doesn't his teacher know that by taking away the times he gets to move will make him less able to do with work at his desk? For many kids, mine included, recess is not a "fun" thing to take away; it is a necessary part of the day. Why would I let the school take away the part of his school day that I pay therapists a lot of money for when he isn't in school? Taking away these things might be counterproductive to what they and you are trying to accomplish!