We modified the logic in case when the coefficient is exactry zero. We show the phase of each FFT segment versus segment number in figure 2. The segment number corresponds to 64 microsec. The number 12500 is the 0.8-sec interval. You can see that there are still phase jumps, 0.6 radians at maxmum, in the modified phase.
Jumps are frequent at large segment number.
Hence the jumps may be due to round-up error in the accumulation. It is not unclear that the phase jumps are correctable or not. Figure 1 shows the fringe spectrum along residual fringe rate, after and before the modification. The sidelobes disappeared and the SNR increased. These results are stable during 4-hour observation.