Brand new 38K, came from the factory with a shattered tile next to the front bathroom where the floor steps up to the bedroom. Dealer replaced the tile and the first time we opened the slide the new tile was shattered the same way. 

Any ideas to prevent this?

We bought our 2015 Expedition in June and it came with the same problem that you are having.  In August we took the Expedition to the Allied Recreation Group (ARG) Service Center in Decatur, IN to work on that and many other discrepancies on our "punch list."  After replacing the tile three times, they finally shimmed up one roller and adjusted the placement of another, both near the step up.  This relieved pressure on the tile that was breaking, and we have not had a recurrence.

They did not fix the gap that we see daylight through where the slide meets the step up when it is extended.  It appears to be a design defect they did not have a solution for.  I'm composing a letter to ARG (Fleetwood) requesting their assistance.