Power Smoothing Not Working

I get intermittent issues with my snap. At the start of a workout I can hardly move the pedals, sometimes my legs are failing within a minute of the workout. Doing a spin down is no help, I shove out about 6-700W, the speed shows about 10mph, then I have to stop. The next day everything works as if there was never a problem, and it will be good for a couple of months then it throws another hissy fit at me. I am not sure if it is connected, but when I get the cadence up before the app reaches target power the beginning of the workout then everything works out fine