Ideas
I had a Sim in a university dorm with a mini fridge and microwave, and anytime he got a quick meal he wouldn't have the correct holding animation for the plate or bowl. He would have his arm down at his side as if he wasn't eating anything. He would remain like this until he finished walking over to the place where he wanted to eat, where his bowl/plate would go to the normal animation and he would continue eating. This doesn't seem to happen with homecooked meals. I'm not sure if this is a mini fridge/microwave bug or a quick meal one.
I managed to get a screenshot of him holding the plate wrong. This is a breakfast burrito, so a microwaveable item. He brought the plate back up once he started eating. This is not only at the dorms because I got this photo at his house. This animation bug does not effect children as I had his younger sister try as well.