That is a very nice bow. Great tiller and great recurves, that is a beautiful job you did! But those cracks are weird. If you heard a loud pop all of a sudden and the crack got alot bigger, even if it started as a check, it is in my opinion a problem that should be addressed. A bow that is made from a piece of wood with an already existing crack/check is one thing, but a bow that is making loud sounds and cracking down the bow is another thing. Bows can be unpredictable, and so can the way grain runs under the surface. I wouldn't chance it, especially on a such a nice bow, when there are very effective means to prevent the possibility that it might get worse or run deeper, run off the grain, etc. A thin one layer sinew backing or a thin rawhide backing (the entire bow up to the recurves) would more than likely keep your bow from breaking if that might happen due to these cracks. I would add, on top of the backing, a sinew or string wrapping in the middle of the crack to be sure. Sinew will in my opinion only improve your bows performance, on top of protecting the bow from any possible tension failure. Thats my 2 cents.