Hi Geoff,
Physical Animation Component is the out-of-the-box solution for motorised ragdolls, we use it to produce a smoother transition into full ragdoll by manipulating the motor strength.
You can reproduce the bug with the dummy character in the physics viewer which also has physical animation component…what’s strange is that even with no active physical animation profile selected (motor strength of 0) i am still seeing the jittering, which would indicate that kinematic targets are still constantly moving (albeit by a vary minor amount).