grout cracked in wetroom

[chud71]

Hey, I did a wet room (up stairs) a few months ago and now have been told now that the grout has cracked and water is now under the tile and grout is stained and coming out!

I put 18mm green chipboard down screwed then 9mm ply screwed every 4 inches then tile safe membrane, topps 2 part flexi adh, grouted with bal flexi grout!
any ideas!!!
Tile feels spongy under foot?

I have been doing bathrooms for yrs but this has thrown me as i have never had this happen..

 

[White Room]

Only a guess, sounds like water has penetrated into the ply, if it has then would have soaked the chipboard, never used the said tile safe membrane.