If StrideScale is 1 the first time through, it initialises the StrideScaleModifierState to 1 and doesn't require updating so leaves the CachedDeltaTime at 0 by never calling Update_Internal, and thereafter can never update because CachedDeltaTime time is stuck at 0 so StrideScaleModifierState will never move from 1 if interpolating is enabled.
But if StrideScale is anything other than 1 the first time, it initialises StrideScaleModifierState to not-1 and updates the CachedDeltaTime, and thereafter will always be able to update StrideScaleModifierState towards the requested value so will be able to update when necessary.