Most 3D printed rocket failures I have seen are usually in the airframe, ejection charge goes off blowing them into several pieces, 3d printed attachment points failing, nosecones breaking mid-flight, every failure has been parallel to the Z-axis layer. I so far only two fliers at our field have proven to me that they can fully 3d print a rocket and it be recovered fully intact (both fly them on J motors). Typically failures on hybrid 3D print rockets a much rarer, usually they stem from an issue with either the nose cone breaking along the layers or the shock cord attachment point at the nosecone failing.
3D printing has many uses in rocketry BUT people need to know its strengths and weaknesses, and how to counteract those weaknesses. Most of my 3D printed nosecones have some form of interal structure to carry the load of the attachment point, usually that structure is a airframe tube inside the nose cone that is epoxied in or foamed in or both, and the attachment point is placed inside that tube, rendering the 3D printed part basically a contoured shell.