We have a glass enclosed shower in our master, that sits on tile, had a similar problem. No issue when the rest of the family used the shower, problem when my wife did. Turned out she would let water spray from the second shower head at the shower ledge while shaving, not realizing this would drip down the glass and eventually leak outside of the shower. It wouldn't immediately drip below the shower, and by the time the water leaked down, the surrounding tile was dry. Simple fix - dont let significant water be blasted at or sit at the bottom of the glass surround.