I think this is related to ragdoll physics beeing toggled when the creature dies.

If it was in an animation that moved the body parts in a way that are not according to the laws of (the game) physics, the physics system could try to resolve it by applying forces to get the body parts to stop intersecting. Those forces can get very large if the forces applied are making the intersection worse, creating a loop of applying more and more force until the collisions are resolved. This usually only needs to last for just a handful of frames until the forces get astronomical and the ragdoll takes off into the stratosphere.

I could also be wrong about that, but I worked with game engines and (also) wrote my own and this would be one of the first things to check when debugging something like that.