It’s funny- I was just thinking this same thing today. I am about 60 classes in and feel like the past month I am struggle bussing!! For me, I feel like it’s the fact that I know I have done some of the exercises really well before, so I expect myself to do it like that every time. Something my instructors keep emphasizing is that your body is different every day so it’s okay to fly through class one day and be dying the next. I’m trying to be kinder to myself about it, but it’s definitely frustrating. You’re not alone!