My VESC 6 produces 0.8 Hz current oscillation on level ground with FOC at max speed. I've tweaked the Observer Gain from the default 17.8 to 9 and 35. I think 35 was worse, but 9 didn't fix it and I feel like I'm tapping in the dark. Maybe someone has seen this behavior and knows the cure? Also, oscillation feels stronger when the battery is full (41 V) vs. 37 V.
Edit: 25 km/h = 28k eRPM