This is during erg mode correct? I wonder if it has anything to do with what “virtual gear” you are in. So on a normal smart trainer, if you’re in an easy gear, the trainer would need to apply more resistance than if you’re in a harder gear. Try shifting up and down and see if that changes the problem.
I’ve had multiple trainers and can definitely feel it when the trainer is adjusting. Like if I have 200W set, I can feel the subtle resistance changes the trainer is making to get my power to 200W. I’m not sure if that’s what you’re feeling but comparing to my Assiomas the max would be 20-30W for maybe a sec, and usually it’s a lot closer. I did have an Elite Direto and at the end of its life I would get swings if 100W above or below as the trainer tried to keep me on the erg target. But it would only happen if I was in the big front ring. Small front ring everything was fine. Which to me indicated that at lower resistances (the force needed by the trainer to get me the correct wattage, not actual power target) I was getting the problem. In the small ring with higher resistance I was fine.
Another thing to think about is pedal smoothness. The trainer is taking your force in the pedals multiple times a second to make adjustments. So smoother pedaling and more consistent power/force through the pedals will make it easier for the trainer and change less.
The last thing I will say is that it’s weird that power smoothing has anything to do with this as I thought Wahoo’s power smoothing was just a software thing to make the power look pretty and not actually doing anything to the resistance. But I guess not.