These things just happen. It could have been a manufacturing defect, or the limb was damaged in some form over the years. It could have been the result of a dry fire. Lots of reasons it could have happened. Contact Barnett they may be able to help you. They may not as I believe they have been bought a few times but you never know. Split limbs happen. It is rare but it happens on crossbows and compounds a like.
Bow shop told me Barnetts were the worst for this.sounds like a common problem on many brands.Fella told me the Parker his father has had the limbs crack while just sitting on stand this year.x-bow only was two years old.