Toon outline flickering during animation

[Neon Junkyard]

I have a pretty heavy scene with lots of mechanical robot models and such, static geo with a camera flythrough, and I need to render it with toon outline.   It renders fine, but I am getting massive flickering between frames during animation

I suspect the problem is there are polygons that are too close together, I fixed what I could but its a massive scene and a rebuild is out of the question at this point.  Toon is a displacement effect so I tried cranking the dicing quality, increased samples etc nothing really helps.  Anything I can do to help fix this? Thanks