Yesterday the quad-copter started to twitch. At first i guessed that one of the motors has to be going bad.
After I looked at logs, I found out that input pwm is horribly amiss. The pich input is like shown in the log at attachment. It stops being like that only if I tilt the RC remote lever.
BUT i was unable to detect this glitch on my rc receiver when using pulse time triggering on oscilloscope.
Also the uploaded log was done when neither rc remote or quadcopter had any kind of vibration or movement. so the bad connector problem has been exempted.
A code issue exists with 2.9.1b depending on when you downloaded... check THIS thread.
Look near the end for details..