Ragdoll character at low FPS goes into A pose

We have a rag doll actor which we spawn in when a character dies. The actual rag doll works perfectly fine, however when playing the game at low frame rates such as 20 FPS the actor doesn’t go straight from whatever animation montage is being performed into rag doll but instead experiences a single frame of being in an A pose.

I believe that the character is stepping over the end of the montage and is reverting to the skeleton’s default pose however I have been unable to work out which function is handling the animation update which is taking the montage over the end.

Any help is much appreciated.