There are a couple of people I know who have already faced this in RC5. In 3.0.1 I see that I do not get issues, so posting it as a separate forum.
I am using sonar (XL-EZ0, MB1200) + baro on my APM 2.6. Using 3.0.1 RC5, I have attached the logs for perusal. "This did not happen before" and happens more with slight winds.
Note: There were slight traces of wind, but this Up-Down movement is very consistent. Goes up and down by same distance every time.
The only thing that I can think of is 'Thr`Mid' set at 596 for hovering, which I have tried to vary in earlier tests with similar results.
Can somebody have a look and suggest why this happens, from the log?
IMU: Vibrations controlled fantastically on my setup.
SonAlt Vs BarAlt: Reading correct values as it jumps and tries to correct.
ThrIn Vs ThrOut, you can see sudden dips. ThrIn (red) remains constant. See the green bars dipping? That is the problem.
Something with 3.0.1 RC5?