Mixamo character gets deformed during gameplay

Hello everyone, I am working on a bicycle race game in which I make use of asset "Motorbike physics tool" from unity asset store to take care of bicycle physics and animations. I make use of a Mixamo character to act as bicycle rider. Generally everything works well, but sometimes the Mixamo character gets deformed as shown in attached pictures. I am totally lost as to what has happened. I am also new to Unity and animations in general. Please help.