What causes tires (245-70 r17.5) to lose chunks of rubber in the center

by Steve
(Ohio)

We have a lot of drop deck trailers. We have been running Michelin zx2. We have had a lot of these tires fail on us this summer. 245-70 r17.5

I was wondering what the thought might be. A lot of them have had chunks out of the center.
Could this be caused by the heat? And if so is there a way to cool them?