Sorry if the answer is buried in the monster 2.9 release thread (there's no search within a thread function here is there?).
After upgrading from 2.8.1 to 2.9.1 my quad now reports a very jittery artificial horizon when connected to the Mission Planner (video capture from MP attached).
This is with the quad sitting on a stable, level surface, no battery plugged in, just a USB connection to the laptop. I did a CLI reset and accelerometer calibration.
Anyone else experiencing this?