A missing training peak can come from exact cancellation in the signed sum. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Opposite signs can cancel
One positive and one negative contribution give amplitude 0.
F=1+(−1)=0
A zero sum gives a missing peak
The intensity is exactly 0. This explains cancellation, not empirical diffraction corrections.