Fourier Transform gives unexpected results: signal reversal and conjugation
Try plotting the signal and the straight reversed signal in points rather than lines and you will see that, unlike with reversal via FFT, none of the values stay the same throughout the reversal. The straight reversal flips the 128-long data around index 63.5 or equivalently around index -0.5 if you think of the data as periodic with a period of 128, rather than around index 0 (or 64) as in reversal via FFT.

According to user David Hoffman's tests both

roll(irfft(conj(rfft(y))*rfft(y)), -1)


and

irfft(rfft(y[::-1])*rfft(y))


work for autocorrelation, roll being numpy circular shift.