I wouldn't say the grouting has failed per se; none of the tiles appear loose.
But every now and then we see water seeping in on top of the grouting. Its only in two specific places (the one near the wall), and then in a separate area in our cloakroom/downstairs WC about 2-3 metres away.
We're hoping NHBC get back to us soon (!).
If not, would you suggest contacting a plumber straight away, and seeing if we can claim back through NHBC or home insurance?