Spikes in CAS graph are due to sloppy plotting
Since the report says that CAS data between 15:45:42 and 15:45:53 was "NCD" (no computed data), another name for "invalid" data, there was no value that could justifiably have been plotted. The values that we see are artifacts, and have no relation to the actual air speed.
Connecting lines should not have been drawn, and arguably even the invalid data points should not have been plotted. They have no significance whatsoever.
In fact such lines should never be drawn, unless the expected rate-of-change is so low that linear interpolation will provide a sufficient approximation.
Bernd