I think you will find that the camshafts are in two parts which are only pressed together. My bet is that they have moved. I know of someone that just twisted one back again and it ran fine afterwards. It was an older engine code on an Astra G but I suspect it will be the same.
HTH's
Bryan.
Just re-read your post and see that you have checked this although you seem to say that the lobes are part of the cam. They are, but the cam is in two half's so it may be worth another look.