I think you should first checkout the steering wheel and if its not possible for you to understand the problem actually, you should ask any of the car experts to check it out to tell actual reason. Power steering loss not normally happens due cold conditions or warmth. This I can assured you from my experiences, I am also using a Volkswagen Jetta, but this not happen to me yet. But, it may be case which happens with you. You should
look here for some possible information or some sort of helps or guidance from them. I hope you can get some solution for all types of problems with your Audi A3 FSI.