Power fluctuating when I ride SYSTM

Hi! My power fluctuates significantly when I ride using SYSTM. I have a new Garmin Flux2 trainer; whether I am in ERG mode or level mode , with and without power smoothing, the power will change significantly, sometimes within roughly a single pedal crank. It does not do it (that I have noticed) at low power like 150W, but even for long fairly steady target blocks it jumps a lot. I know it is doing it so I focus on keeping my cadence and I can feel the load go up and down. Any ideas? It turns steady efforts into over/unders!!