My uncle's kitchen tile did that on a slab from the 60s... just a slow creep over a year until the grout lines didn't match up. It feels like a lot of old building materials just have a life of their own and modern stuff doesn't always stick, literally. You see it with paint peeling off old plaster too.

The recaps are basically a map for a show that's a maze.

That speed is wild. Makes you wonder how many heats they could run back to back before a full reline.