I 've got an issue on an octo build : an explained drift in loiter mode (seems to the right each time but could have been the Wind at that moment). Stabilize is fine.
I've looked in the log and I see a discrepancy between X, Y velocities and Desired corresponding velocities, which is indeed a sign of a bad loiter. But Why ? Accelerations are perfectly fine (AccZ) is contained to +/- 0,1g, compass calibration has been redone and is fine, using an external 3DR GPS+MAG. The frame looks fine too (nothing twisted, everything solid).
What could be the cause ? I need help of an expert on this. Log (and Tlog for vibes) attached.
Please note that the firmware is still an old one : V3.1.2 (NOT to confuse with the most recent one V3.2.1)