I have had problems with GPUs this year in situations you have described, and a couple of others. It is a new problem for me this year, as have not had an issue with GPUs getting "lost/misplaced" before this year.
I now monitor my GPUs and you also need to monitor the refund for the LHR airport tax if the GPU does not work, and yes many of the agents are aware of this - well at least when I call about them they do not act surprised.