Possible explanations for UFO material brittleness:

1. When you integrate diff kinds of lattice materials together into quasicrystals and those diff crystalline materials have differently Bravais lattice geometries / different lattice constants, there’s a high degree of lattice strain on atoms and they frequently become dislocated, other atoms diffuse through the lattice and you get large disjoints in the crystal called grain boundaries.  Outside of metallurgy, grain boundary density generally increases brittleness because the lattice geometries inherent to non metallic lattices can’t absorb the energy strain.  So generally, putting “unlike” crystal structures next to each other and creating lots of grain boundaries is actually a well known mechanism for driving material brittleness.  The outcome is the materials aren’t long lived in general and the technology will use itself up and eventually become nonfunctional.  It’s disposable, short life cycle. 

Open Question:  is this a fundamental limitation of quasicrystal engineering that even “They” have to deal with, or have They solved it, and those materials we are recovering and observing this in, poorly reproduced human facsimiles of their technology?  If you had complete mastery of quasicrystal engineering, you may be able to use gradient materials that graduate parameters like lattice parameter and strain, from one material to another, to either dramatically reduce or altogether eliminate this problem.  We have an analogy in aerospace where we use graduated gradient layers in coatings to match coefficient of thermal expansion from say, a metal to a polymer. 

2. Creation of torsion waves may be the culprit.  If the lattice is generating 3 dimensionally emitted torsion waves and subjecting itself to torsional tidal forces, this may over time, exert so much differential stress as strain on the lattice that it generates grain boundaries and weakens.  Same caveat applies - maybe this is a fundamental inescapable limitation of the technology which makes it disposable or maybe this is the result of imperfect reproduction.