You are not drilling where you think you're drilling.

As you now know, that's tile backer/cement board, which is underneath the tiles in your picture.

I mean, maybe your goal is to run cat 6 up through the middle of the floor, idk, I prefer it being in the the wall myself. Or maybe the 'target' wall was built on top of the tile? Crazier things have happened.

You need to make some sanity checks here and measure out where to drill 3 or 4 more times. Or open the wall where you want the wires and drill down.