The poses work fine on IMVU classic, but they're kinda too shaky on imvu next and imvu mobile. Is there any fix for it?

Those "shakes" are random deviation jags, offsets. They are randomized movements to confuse IMVU's automated AI security and prevent it from recognizing the poses as sex animations. Without those jags, IMVU's AI would recognize the pose as sex and it could get your account / product removed.

The offsets are added by the hash offsetter. The lower the strength you set the hash offsetter to, the smaller and fewer the jags there will be. The higher the strength you set the hash offsetter to, the larger and greater number of jags there will be. Higher strengths are safer. Lower strengths add more risk.

I made the hash offsetter in 2015, back when everyone only used classic; the jags were designed to be too small for the human eye to see. Next and mobile seem to lack the smoothing algorithms that classic has, so the jags are more visible on those clients.

No way around it. You can just reduce the issue by using a lower strength. I would not use lower than 40% strength though. Too much risk.

Oh wow I wasn't aware of this, thank you