When I notice the abrupt surge and decline in message rate and a whole bunch of other metrics in graphs1090 on one station, my first instinct was to dismiss it as a statistical artifact due to something akin to division by zero. But then I looked at my second station and had to give it more consideration. Positions per second in that short period far exceeded daytime peaks, message rate/aircraft shot to over unprecedented 2K. CPU utilization also corroborates that a real surge in messages happened.
I have no reason to believe that a hundred planes just decided to take flight. What can explain the metrics anomaly?