The flight plan indicated the feather should be unlocked at Mach 1.04
That should be Mach 1.40, not Mach 1.04.
There will undoubtedly be some human-performance analysis to see if one of the pilots saw 1.04 and got it confused with 1.40. However the latest NTSB briefing seems to indicate that the unlock happened prior to reaching Mach 1.02.