Tile Failures and Problems

I have a shower remodel completed last December, the tile used is white honed carrera marble on the pan and walls. For waterproofing I used the full Kerdi system, sheet memrabne on the walls and pan (over sloped mud bed), to a linear Schluter drain. The shower is used infrequently (only when guests or the homeowners children are in town). The homeowner sent me these photos after it had been used recently. To me it appears the waterproofing system is doing its job (even considering known issues with Schluter linear drains). I saw the post regarding discoloring of marble pans but the pan doesn't seem to be discoloring like the walls. Has anyone experienced this? My initial analysis is the wall tile may have been cut too tight to the drain body (drain body is tight to back wall), essentially not allowing water to escape at the bottom. Looking for 2nd opinions/confirmation though before I go ripping into this thing.