Just a shot in the dark, but are you cutting lines into your grip after it's on your board?
Cutting a line in your grip while it's already on your board will cause you to cut a line into your deck, that will end up being a weak point for the shit to break.
I learned that the hard way years ago.
Either way, that delamination is s sure sign of shogddy craftsmanship.
Any board that delaminates is defective.