Need support with standing shower

[beezy]

I need help understanding how the tiles at the foot of my standing shower broke off in a weird way. As the pictures (below) show, it's at least a 1/4" tear that separates the tile. The odd thing is that if I try to push the tile to fill in the gap, it doesn't budge at all. Any ideas on how to fix this guys?

 

[FishScreener]

My guess is that there is wood in there, and it has swelled.