This occurred for the same reason Randy gave above and was triggered from the GPS Glitch. Plot NKF3.IVD, NKF3.IPD and NKF4.SV and see for yourself. There are links in his post for how Vib compensation is triggered.
Seems like I have seen that somewhere. But Mission Planner will give you a brief description when you hover the mouse pointer over a log parameter. Shown here:
I too used to use APM Planner for log analysis but with the latest versions if Ardupilot and/or large logs it crashes as you say. I have mostly given up. There is a new Rev but no Windows Installer.