The reason why the tombstone cracks is because the tombstone itself is made of irregular stones. From being processed into a tombstone to being placed in a cemetery, it has experienced many external forces, as well as wind and sun, heat expansion and cold contraction. There should be cracks inside the tombstone before it is placed in the cemetery, but you can't see it. Look at the stones on the mountain, many of them are layered, because they are squeezed by external forces and cooled by heat.
This is also the reason why the cement board cracks. At the beginning, the proportion of concrete, sand and water was not suitable. Cement board will crack if it is not replenished in time after dehydration.
Both of them have nothing to do with feng shui, so there is no need to move the grave.