Parachute Problem

I use a parachute with 100% size and make the radius as small as it let me. But even though my speed is lower than the threshold, when i activate it, after a few seconds it starts to vibrate and snaps.
In the tumbnail i have 200m/s speed (snap threshold is at 380m/s) but it still vibrated, made 10 times the actual drag before vibration, and snapped :(