Its because of a rubber mat. I read it on the maintenance info in the box that comes with some lvt's that you cant use them.
Did it all get wet ? Just had a problem with a flood on some Forbo Sarlon with protection down, turned all the vinyl silver, but only where the protection was on the floor, I though it had to be the protection leaching into the vinyl, but Forbo then informed me that water gets under the wear layer, above the image and turns it grey, they said it would go back to normal over time, Look at the picture, you wouldn't think it would happen
That picture there is no water damage an sub floor under the planks are dry. The customer has took some planks up in the kitchen which is highly damp still. So going to be a while before I can touch it.