How to prevent end grain checking on Ipe deck boards? Mine are splitting at the ends

Installed an Ipe deck last spring (5/4x6, face screwed with stainless). Six months later I've got checks and splits developing at probably 30% of the board ends, some running 2-3 inches in from the end. Used Penofin oil finish, maintained it. What went wrong and how do I prevent this on future installs?