Sorry, I haven't been on this forum in quite some time. All I can do is state my own experience. I have three SX1's and two TR2's and none of them have cracked in any way.
Also, I have a friend who is a rep for a major distributor. I asked him about this and he told me that Motiv has less warranty claims than ANY OTHER BRAND. Certainly, there will be issues with cracking with any balls. It could have been a bad batch.
I'm certain that you folks do this, but just in case make certain you bevel all of the holes. That includes fingers before you put in inserts and the balance hole.