Thanks for the response and good point about the prearm checks - I’ll ask around why we have them disabled. I know that there’s another prearm check layer in our companion computer but it probably doesn’t check everything.
Anyway, I have checked a few other logs from the same drone earlier this afternoon; the bias and the difference were still there consistently but otherwise it flew just fine. (I’ll check the PD innovations in a normal and a faulty flight later tomorrow).
Could it be the case that it’s mostly using the IMU2 Acc in these cases? Is there a parameter that would tell which accelerometer the EKF is using or how it is weighing them? The documentation seems to refer to a parameter named “Ratio” in the EKF2 log message (here: http://ardupilot.org/dev/docs/extended-kalman-filter.html ), but as far as I know the EKF1-4 log messages were superseded by the NKF1-10 messages in some earlier version and I can’t seem to find anything similar in the NKF messages.