Time lag of Baro, aircraft crashed. Why and how I can fix it?

Hi everyone!
Yesterday I tried the autolanding function of the ArduPlane v4.4.0 beta1 but the aircraft crashed because of no flare before touching down.
I checked the flight log and found that the baro altitude had a time lag of about 2.5 sec. Attached you can find the time history of the landing. You can understand the toutch down timing is by the blue line vibration data. But at that timing the aircraft has about 4 meters height above the ground. Altitude data show to decrease after touch down and they take about 2.5s econds to reach zero.
From the second graph you can understand the GPS altitude is almost constant after but the baro altitude continues to decrease for 2.5 seconds.
I believe this is the baro data time lag. Can anyone teach me the reason and how I can fix this problem?