Assuming he has no wings/isn't adult, and you are not feeding prey items too large, my next suggestion would be do a major humidity drop. Sometimes it can help to give a flying insect like a fly or moth since those tend to really stimulate mantises appetite, but a week off food doesn't lead me to believe that is the problem. Hand feeding is always an option too though if you think he wants to eat but is having problems. Just pop the head off and gently touch the gooey part to his mandibles. If he starts to chew on it but then keeps pushing it away or turning his head than chances are this is another issue.
Some praying mantises need it really high before they will go for a molt and will seemingly put it off waiting for the right condition. I had one boy long neck who was going just fine, like his sisters and then all of a sudden pre-sub adult shedding he went off his food for over a week. He was giving off all the signs he wanted to molt but wasn't getting anywhere. It caught me off guard because he had never had problems prior to this. At one point it was looking like I was going to loose him because he was starting to look really weak. I kept upping the humidity for him and finally went so desperate one night I took his cage and put it in my glass shower when I was done. I take super long, hot showers. I left him in there about a hour, before removing the cage, and literally five minutes later he popped right out of his skin. I'm not suggesting go extreme that quickly, but please do give him a little extra humidity/misting.
If you normally mist in the morning/day, I would also make sure to give a nice mist before you go to bed. Most mantises like to shed at night so it helps if that is when they get the humidity dip.