Would it be possible that you decreased throttle by accident when looking for the man flex detent? I notice how the detents are pretty bad to get/stay into as they seem to be too sensitive. (they’ re missing blind spots like in the CRJ)
It’s possible the aircraft then thought you ment to abort the takeoff and bring the engines to idle. Though it should have also activated maximum braking power and full spoilers to stop the aircraft on the runway.