@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.
Aside from node screenshots strewn throughout the thread, there are files for a spine rig and a non-linear shape keys rig (also some tension map test files in this thread in case you missed it).
Thanks for the tips!