Several Tern models of these years (the used one for which the discussion was started was from 2013), including the X30, had a manufacturing problem (and maybe a design problem) that was eventually recognized by Tern, there is no doubt and discuss anymore about that.
Not all broke but all may eventually break.
As often with folding bikes, some owner ride them very seldom and only for short distances, these didn't broke yet. They may break for instance when sold to a new owner who really ride the bike.