I think they might be too thin. Especially near the bead holes, and that's where the crack probably began and it makes sense that it would travel down the center of the bead from that start at the hole.
Are you using 3/32" mandrels? Try the 5/64" and see if there is a difference. Or use the 3/32" but press to no less than double the thickness of the mandrel on both sides. Now I'm thinking that it may not be your glass combinations at all. So maybe we should narrow it down to mandrel size and then finally, the bead release.