It seems the knifes are broken, since you can not cut the seeds out of vegetables or meat out of corpses. Futhermore you loose significant amounts of food when opening a cann with a knife of in this patch ( from 50% to 75% will be wasted, before it was ~ 5% wasted)

Oh I did not know there is also a chance to fail to craft the knife itself. If so, I am sorry to report it as a bug, but then the game could give you a message like: " I have failed to craft a stoneknife". But I can not imagine it is supposed to fail, since there is already a chance to not find a stone when searching for it.