Recently I've noticed that two different showers in a client's house have damage to the tiles, only on the floor - not the wall tile. The tiles had been in place for a decade or more with no problem. Both these separate showers showed this damage recently. Of course, no one is admitting having used any cleaner other than ordinary mild cleaners, though I doubt that.

In one shower, the tiles show very pale to chalk-white marks. They don't come off with any degree of scrubbing, or use of hydrogen peroxide or CLR (lime remover) or mild cleaners.

In the other shower, the blemishes are wide stripes where the tiles look matte (where the non-damaged areas are satiny)

Does anyone have an idea what's happened, and how to fix it? THANK YOU!

Here are photos:

Shower 1

Shower 2