Paul,
My V curves on the Ceravolo are fairly symmetrical. I'm getting more (but not incredibly) consistent PID and much closer agreement between left and right slope on each curve than you are at a similar focal length. I doubt it's my exceptional seeing
I'm sure you've already checked for any mechanical issues but worth check again for anything that might be flexing or moving.
How's your collimation? Does a defocused star look the same inside and outside focus? Something weird going on there could give rise to odd looking asymmetric curves.
Cheers,
Rick.