I had the mod stored in my vault inventory but never used it, once Shadowkeep went live as I was assured it would be reusable. I put it on a gun to use in an activity (mostly just to test it out) and after the activity was done I put another mod on the gun but the Taken Spec was no longer in my inventory! This mod is incredibly rare and though Taken are not currently in any of the new activities this is really disheartening to lose it so easily. I doubt I will ever be able to get it back now.