The asymmetric distribution of geometrically equivalent defects is a longstanding problem in materials science. In this study, we investigate the preferential nucleation of interstitial dislocation loops in specific planes in stressed aluminum, commonly observed experimentally, and seek to clarify the underlying mechanism. For this purpose, we consider a structural change in the geometry of defects, specifically the transformation of 3D compact A15 clusters into 2D Frank loops. Using object kinetic Monte Carlo and ab initio calculations, we show that a symmetry breaking in the transformation of A15 clusters significantly impacts the dislocation loop distributions, resulting in the emergence of a preferential orientation when the material is under stress. This discovery not only calls for a critical revision of established theories but also has tangible applications for materials under extreme conditions.