SMA has polymer at the mating surface and polymers typically have 10x the thermal expansion of metals, so vibration momentarily unlocks the screw and polymer pushes it apart.
This is a general problem with threads. Any combination of thermal expansion/contraction and acoustic/vibration energy input that momentarily overcomes the static friction will loosen the connector. This is why torque wrenches, locknuts, loctite, and safety wire are a thing. If a connector hasn't been engineered for a certain vibration environment and installed/torqued to specification, one should not be surprised when it fails.
Someone should get Boeing in this thread, they evidently need to hear this too.