Looking at the Tern bikes web site it appears there are three types of frame latch. The original OCL 1.0, the later FBL latch that had hidden sections that fitted into keys as the frame was folded presumably to keep the whole bike more rigid. The latest version is the FBL 2.0 which is what I have on my folder (not a Tern) where the back section envelopes the front piece to make an even more secure lock. I wonder if any of the newer frames with the latest hinge have failed.