Had a similar problem on me 998, split second cut of the spark/tacho, only happened on track as far as I can recall and much higher up the rev range.
I used to think it was me bouncing the motor off the rev limiter as I made up for my lack of talent on the corners.
It used to happen very occasionally but sometimes when it did it would happen a few times in a day. Used to think it was linked to low voltage as the tacho could be made to go to zero by putting the battery under load with the lights on full beam.
It doesn't happen often enough to warrent too much worry and the problem seems to have gone away after a new battery was fitted and some partially fried wires near the rectifier were replaced.
If it was still doing it, or doing it regular I'd start looking at the crank sensor, or getting someone else to.
Ray.