do we have any tilers or plumbers here?

[sheddy]

If this was fitted a year ago, the shower tray should have had (or be fitted with) an upstand, which is a section that is fitted with the tray before the tiles are placed, and prevents any water from getting under the tray.
If the tiles are loose only a year later (and all tile adhesive is waterproof these days) then you need to have the bottom (2 ?) courses and the tray oot and find out what has happened. Be prepared for a rotten floor....

 

[mickle]

You don't need an upstand to make a shower cubicle water proof. From the description of the loose tiles we can assume any or all of the following;
That the surface of the board forming the tiled surface wasn't prepared correctly.
That the tile adhesive wasn't mixed correctly.
That insufficient adhesive was used.
That movement in the shower tray (caused by poor setting or a flexible floor has exerted undue pressure on the tile course).
That a silicon filled gap wasn't provided between the tray and the lower course to allow for tray movement.
That the holes through the tiles which provide feed to the shower haven't been sealed.
That voids were left in the grout allowing ingress of water.
That the feed to the shower is leaking inside the wall.

 

[bonj2]

yeah, just rip it out and whack a new load on. can't be hard. OR, alternatively, dremmel the grout out, sand the tiles, varnish them, and regrout. Perfect finish without having to bother with new tiles.