was this perhaps part of the flight testing regime?
It'd be interesting to see if this was part of the test profile, to determine performance problems or recoverability issues with an unlocked descent mode. Like pilots deliberately entering flat spins to determine recoverability of new jet designs.
Could still be a malfunction. Just because the software records the system set to "unlock" does not mean the lever was thrown. A short anywhere in the system would read the same, and if the unlock level is "fly by wire" there are plenty of places where an unlock command could be inadvertently set.
I'm still kinda surprised the mechanism that rotates the tail had enough authority to force them into reentry position at that speed.