Hi Phil,
It is a while since I checked in on this post due to general hectic, and we are still wrangling with various parties about who is responsible. I am assuming that when you laid your problem mat you observed all the standards in terms of subfloor preparation? A concern I have is that as the plywood is only 9mm that this could be a contributory factor even though it is pretty solid on the boards, and one that Genesis have cited as they have visited site now. Although to be fair to Genesis they are not just walking away from the problem, and are trying to be helpful, but they have not admitted full liability either.
What did you do to rectfiy the situation?
Rob