I'm trying to be helpful but again I've got no experience with that happening.... the only problem I've ever had with eyelets is when i was first starting out I pressed them while the kydex was still warm... no good, they press right into the kydex (recess). More thoughts on your problem:
I'd try to narrow it down to one of two areas being the "problem child"...it's either your eyelets or your dies.
1. Try a couple more and see if they don't crack in the exact place meaning if the firs one cracks at 2:00 and the next one splits in the exact same place.... maybe it's your die. If it splits in a different place then maybe it's your rivets.
2. Eyelets come in several sizes... are you working with .060 kydex and using larger eyelets? If so they'll over extend and start rolling down on themselves... just check and make sure you have the right combo. I switch eyelet lengths depending on the "combined" thickness of my kydex... example... when joining two pieces of .080 eyelets required are about 1/4"..... joining two pieces of .093 you'll need a eyelet length of about 5/16".
Hope this helps, if all else fails call Knifekits and let them know what's happening. I remember how disapointed I was when I got one of those eyelet presses and found out that all they did was drill a sloppy hole in the bottom plate.... the plate just sits there... no real "machining" was done.... no exact science just a cheap-ass Harbor Freight 1/2 ton press with a hole drilled completely out of center and in no precise fashion.... sorry, it's late.
Godspeed,
Eli