You’ve got a stretchy spline IK setup, but the end joint doesn’t ALWAYS have the same location as the last cv in the splineIK curve (when it can’t solve it, I guess). This is part of a control skeleton.
Should I:
*) try to constrain / utility node the end joint so it’s always on the last cv.
*) ignore the last joint, and just put in a “fix” joint that’s constrained to the last cv location, then use that fix joint for controlling the bind skeleton (instead of the original last joint in the spline IK)
Have you ever tried a Ribbon IK setup? (A technique that I believe Aaron Holly pioneered.)
You place follicles along a nurbs surface and parent joints to the follicles, which then skin your geometry. Then your control rig skins the nurbs surface.
Depending on how you set it up, it will just stretch by default and between each segment, whereas a spline IK will slide along itself, which is why you see the end joint moving.
Otherwise, maybe you could make a higher-resolution spline IK (so it is more accurately bound to the curve) and then control that with a lower-resolution spline IK. Not too tedious to animate, but you have finer control underneath.