Did you apply the linseed oil and CA mixed together for the first coat? If not, then that could lead to separation of the CA. There is a technique where BLO and CA are actually mixed together as they are applied (dollop of oil, followed by a bit of CA, then you apply them together so they mix). This creates a cross-linked polymer of both the CA and the oil, which fully bonds. If you do this, you want to do this for each coat, not just the first. In my experience, the finish is a little bit softer than CA...more flexy, but not quite as durable. It won't scratch quite as easily, but it might get gouged if the pen takes a good fall, whereas CA only might scratch more easily, but won't gouge or dent quite as easily. I've done a few BLO+CA finishes (and also tried other oils, non-drying oils, to less successful results), but I generally just resort to pure GluBoost CA finishes nowadays.
If you are going to use an oil base coat, at least in my experience, its best to friction polish that in pretty good first, let it set for a while, then wipe off any excess, before applying the first coat of CA. For that first coats, THE MOST penetrating CA you have (i.e. GluBoost green ultra thin) is best, as even with the oil, it will still penetrate the fibers decently. This helps ensure the first few coats get a good bond to the wood. Then you can switch to medium or thicker CA for whatever buildup you want.
Finally, moisture in the blank can be a real enemy of CA. While it can help it cure faster, if the wood is not entirely dry, as the wood moves as it loses moisture, or if the water gets very cold or hot, you could have separation like you see. Depending on exactly how you applied the oil, the two together might compound the issue.
