Shower Floor Grout Looks Wet

Had the guy who remodeled the shower come look at it.
Shower floor grout looks wet. Hope you can help. The floor is tiled with large 60x60cm porcelain tiles laid on impey waterguard membrane and the shower tray is impey aquadec easyfit with the membrane laid over the top. The bathshower sits on normal wood floor boards while the tiled floor sits on protected plastic water proof base. We had our guest bathroom shower remodeled one year ago 2 weeks ago my wife noted shower floor grout wet around the edges with some spots dry.
As soon as we started using the shower the grout again started darkening like it was wet. Click to read complete blog post. Its a large bathroom approx 150 sq. So we stopped using the shower let it dry out for a few days until the grout lightened up and then i resealed again.
Ft shower is 5 by 3 there is a very strong fan that is on timer and is on for 30. The tiled floor has been laid for about 2 years and this problem has only just occurred in the last few weeks. It is a new build first floor bathroom new extension on older house with a. Some grout has a sealer additive already in the mix.
Epoxy grout is the best choice for showers because is water and stain resistant and requires no sealing. The wet area is not caused by using shower as the shower screen protects this space. 48 hours later the spots are still looking wet but are not wet to the touch. We had a wet room installed about 8 months ago.
Keep in mind the lighter the grout the more it darkens simply from the humidity of the shower. He opened the wall to adjacent closet in the next room to assess the shower pipes and no leaks found. If this isnt the case with yours you should allow grout to dry completely clean it with a small rotary wire brush a little dremel works great.