I've built a couple bows that had streaks.
It's this white woods had small knots, Knots don't even have to be seen some times. But I 've seen the streaks comeing from small knots in white woods.
I'll bet you stored (seaoned) your stave standing up. Doing this the green wood haveing a known even hidden knot. The streaks show up. I guess it's mimerals in the knot standing up the mineralls just follow the grain down. I just know some white woods get this streak it stood up.
Not all, I seaoned a whole lot of white wood staves standing when I started. And had a streak now and when.
Now I rachet strap down and deflex to all green staves. So I hav'nt seen this in a long time. So I just asumed that was the problem.
Good thing is I can't see where it affects the bows performs.