So, I help a lot of young guys on different sites with board bows, and, well, set happens. Oak bows just seem to take set, and I'm sure, as mentioned that some of that is down to varying densities. But, here are a couple other things I see. Maybe you do these, and maybe you don't. :-P
A lot of board bows are pyramid bows, but I see a lot of them bending too abruptly off the handle. Too much in the first 1/3 of the limb. A lot of guys seem to expect them to be thicker than they end up and bend them too much when they are still too stiff. A lot of guys are way to eager to get a string on it, too. A lot of guys are afraid to trap a board bow, because they don't trust the board. And, finally, a lot of kids back their first board bow with fiberglass tape or linen, and with nthe confidence the backing gives that the bow won't break, they horse on them way too hard early.
That's all I got. Most of that probably won't apply to you, but good luck.