Could stem from material, CA has a tough time adhering to some oily woods as I'm sure you're aware. But the thing where I see this most often, at least for me, is if I get a little bit of "lift" on the ends of a barrel at the end of the finishing process either from a) snapping of the bushings that became stuck to the barrel from the CA finish (I don't do it this way anymore, I always apply the CA between centers with no bushings), or b) if I get sloppy applying the CA between centers and too much runs over the end of the barrel, sometimes in the process of sanding that off I'll cause the same problem - just a little bit of lift. Once that happens, sometimes it expands - no solution but to sand it off and start over with the finish. I'm getting better at getting my CA finish just to the edge with not much slop running over the end - but getting a perfect finish to the very edge has been by far the most nagging thing I've dealt with over the past 2 years...