Stability of feathers against aerodynamic forces
If the hydraulics on the feathers can be overpowered by the aerodynamic forces (with the locks off) it’s odd that a system that would fail at Mach 1.02 is judged fully competent, with margin, at Mach 1.4. It seems unlikely that the aerodynamic forces would change (reduce) by a factor of many over a relatively small speed range. It also means that at lower speeds the unlock lever effectively had a label ‘move this lever to destroy the vehicle’.
If the locks were required to be in until just above the feather speed that would indicate a feather hydraulic system with low torque, but that is not the case.
At the moment the stated facts are consistent with a failed hydraulic system that could not provide the required torque when the locks were removed. If so, the fact the system was unlocked early is irrelevant.