Leaky tiles can be found anywhere where there is water.
Water leaking through tile grout.
The grout joints are porous so water can go through the grout and under the tile.
Check the ceramic tile walls surrounding your tub or shower.
They may have waterproofed the underlying deck but they could have made mistakes.
The best way to tell if.
The shower water leak should be repaired quickly otherwise the buildup of stagnant water will lead to mold and damp under the tiles.
Maybe a plumbing leak or maybe the drain is restricted in the shower and water is not allowed to fully drain away.
There should be proper flashing the membrane should be sloped to a drain that has weep holes to allow the water through.
This tile needs periodic maintenance.
If water is oozing up through the grout joints and it is becoming moldy then water is not able to drain away.
It appears you have some sort of leak.
Leakages in the shower are most often the result of grout failure.
If the grout becomes damaged on the floor it will give water a chance to slip through the gaps and under.
What are the causes of water under a tile floor.
Can shower water leak through grout.