The movable.sed doesn't just contain the keyY, it also contains a carbon-copy of the LFCS_B ( https://3dbrew.org/wiki/Nand/private/movable.sed )
Are you giving out LFCS_Bs via direct link here?
EDIT: Actually, by giving out a movable.sed with a bad LFCS_B in it, it will mismatch with the LFCS_B...