Good luck.
My best fix has been wide limbs, especially inner and middle limbs. Also, in a flatbow, leaving the limbs parallel and full width out at least halfway up the limbs, at least until final tiller. It seems the best thing to do is give the limb a REASON not to bend sideways, but only forward and backwards. At 2" wide and only a half inch thick, it's likely not to bend sideways, unless the limbs twist like mad or the tips are way out of alignment. If the limb is 1-1/4 " wide and almost an inch thick, it's going to lean just a tiny bit sideways, and flip.