Big mistery

[onevision]

Please check the following pose - it's from Bbird's "Femdom Handjobs" pack (VX conversion from 7.5, actually) and contains a few edits I made.
It's still very much incomplete since I decided to rebuild from scratch the animation for hands and a few other details.

In order to smooth the spine movements of the original pose, I changed the initial Arched/Vertebras key values and removed all spine keys from the remainder of the timeline. Well, it turns out that this is not enough, because the spine jitter is still there, starting at frame 2. Link problems are ruled out, since the pose is disconnected. I cleaned and scanned for errors the file in TKX_Utils, to no avail. I guess some old track is still affecting the pose, and it's invisible in the editor (if that's even possible, but I have no other clue). The only workaround to fix this problem is the tedious process of copying the (legit?) keys one by one in a new pose, each time checking the result. I'm still working on it, so if you have some useful hint please share what you know.

Attachment contains:
- the original pose converted to VX
- my partial edit (still bugged)
- same as the second pose but keys migrated manually from the key editor, still incomplete.

Save.7z

[Tipsy]

Checked the poses. Didn't detect any jitter. You could try changing the spine length of the model, or any other parameters that affect the spine. Sometimes they greatly affect the animation of the spine.

[onevision]

@Tipsy Well, maybe jitter is not the right term, but in the second pose the spine keeps moving, while clearly should not (no spine keys at all).

Upperbody and Hip values were simply copied in the 3rd pose, and there they didn't cause the distinct arching you can see in pose two.

Spine length can be a problem yes, but this pose was created for default spine, I'm sure of it. I tested the third pose with a "default" model and it looks fine.