I know nothing about OS, but I have had something similar happen with other small hard species like lilac and some little lumpy bush with lots of knots I can't ID, and once with a white-wood elm that had TINY growth rings.
In each of those cases, I figured out that I had harvested the wood in the early spring, when the tree had JUST started laying down summer growth over a new winter ring. The summer top ring was almost paper thin, and checked like that all over the stave, but mostly the checks only ran into that winter ring. Lot's of them, but not deep. I scraped it off, and it seemed good, but they had thin rings anyway and one had knots all over, so I don't remember getting a bow out of those.
The elm only checked here and there, so I worked around it, and when I started flexing the bow during tillering, the thin summer ring cracked everywhere and the back of the bow started flaking off, like an eggshell, so I had to chase the next ring down and shorten the bow.