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I doubt you have a ground issue. All your other sensor signals look super-clean. Now MS does do a lot of smoothing on the analog inputs, so we can't be certain, but I really don't think its ground.
My money would be on crank or cam sensor.
VSS is a digital input. So you either have the input or you don't. So if your speed randomly drops to zero then you might have a ground issue, but I doubt it.
Your lost sync reason is 32. Which means the megasquirt didn't see the cam signals.