@julperado After a quick test I wasn’t able to reproduce the spikes, so I’m not sure exactly what’s causing them now… but I’ll try your suggestion if it happens again.
@Salve I abandoned the wrinkles for the time being since the addon wasn’t supporting shape keys, but assuming that’s no longer the case then it might be time to revisit (after I’ve dealt with some more pressing matters).
If I recall correctly Stress only works with the now defunct Blender Internal renderer. Hopefully one day that feature will be restored in Cycles.
Thanks for the tips!