I have seen this before on several boats, including my own. In extreme cases a crack from nearly bow to stern. I think it is a design flaw and the boats are not quite strong enough in this area. I was able to catch it early on with my boat.
My solution - I added 5" access ports behind the front crossbar and then added a couple layers of glass inside the hull. The outside of my hull was similar to yours in that it had a slight "buldge" maybe 6" long. Inside the hull, the inner layer of fiberglass had visible crazing marks in the buldged area. In addition to reinforcing with fiberglass, I also changed my setup process so that now I step the mast with the boat on the ground and supported at the tip of the bow and under the rear crossbar, rather than on the trailer. I suspect that somehow with the trailer bunk being almost directly under the front crossbar, the load from stepping the mast is concentrated right in the front crossbar area and causes over flexing of the hull leading to a bulge and eventually cracking.
Securing the boat to the trailer with heavy duty ratchet straps or letting heavy snow accumulate on the boat are other possible causes of this damage. I tie my boat to the trailer with basic line using a trucker's hitch and store my boat inside in the winter.
In any case, since I made these changes (more than 5 years ago), my hull has not gotten any worse.
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