Removing white marks from black bathroom tiles

Hi, In the space of a couple of weeks my beautiful gray/ block stone bathroom tiles on the floor of the shower have developed white spotty patches in various locations. What are these marks ? Apparently we have soft water and thus it’s unlikely to be calcium or hard water stains.
I did change my cleaning product to a cheaper supermarket brand with no listed ingredients so perhaps the product has penetrated the stone tiles?? It’s just strange that it only appears on certain tiles. Can anyone help? Can the marks be removed or the tiles resurfaced ? I’ve tried detergent, vinegar and scrubbing hard but nothing seems to work. Any help or product recommendations would be greatly appreciated!
 

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