It's almost always a case of keel bolt attachment, torque, age, and decomposition, of the bolts and various other materials which is often plywood in the keel stub.
It's always amazing that people do not want to know and will circumvent anyway they and others can dream up to hide the actual problem.
No matter what you do fiberglass will not bond to iron or lead it will stick but it will never Bond like fiberglass, epoxy and polyester bond. And if that is not enough a keel to hull joint is a mechanical joint and subject to some movement, hopefully none but it is the nature of that type of joint..
So as they say; "you can hide but you can't escape" (the actual problem)