I’m running an MTF -01 optical flow + rangefinder setup on a small quad and getting inconsistent EKF behavior and position drift. The main issue is that the EKF position begins drifting several meters immediately after arming, even when the drone is essentially stationary and motors are barely spinning. I’ve have seen EKF vertical position variance go unstable (large positive/negative values) and get messages like “Error pos vert variance”. I’ve tested at low height with good lighting and texture, improved vibration isolation, verified rigid mounting between flow sensor and IMU, and tested with and without nearby servos (no change). I adjusted EK3_FLOW_M_NSE and EK3_FLOW_I_GATE to conservative values with no improvement, and tried both baro and rangefinder as the Z source (rangefinder looks more accurate, baro drifts). Loiter looks somewhat smoother than Stabilize, but the issue persists. I was able to achieve a few stable hover flights , but cannot make it reliable. It seems like the EKF is inventing motion right at arm, possibly due to optical flow spikes, yaw/heading issues, or something changing electrically or in the estimator at arm. Looking for insight on how to resolve this issue to get a repeatable flight.