Not holding heading during flare? .bin logfiles provided

Arduplane 4.0, Pixhawk4, Rudder-only airplane.

Any thoughts/diagnosis/suggested tests would be much appreciated!

Logfile, bin format, here:

Stall speed in this configuration about 7 m/s (see below), so I set up TECS_LAND_ARSPD to 10 m/s.
Approach is pretty stabilized landing stage 1. Airspeed and heading look good.

See 15:10:12.5. However when landing stage changes to 3 (which I think is the flare stage), throttle goes to 0 (which is correct), and rudder output suddenly goes to 0 (which doesn’t seem correct), and the plane veers off to the left, then veers to the right. I suspect something about a rudder-only control loop failing when in the flare. Why doesn’t the autopilot keep heading in the flare like it does in the approach? I think the rudder authority in the flare, with idle throttle, is sufficient (see below where I do manual landings in the same configuration and can hold heading just fine all the way to the ground).

Another attempt 15:06:41 ended in the plane rolling too far to the right at 15:06:48 (and I switch to manual to recover)

Any thoughts/diagnosis/suggested tests would be much appreciated!

Another logfile, here,
has power-off stalls (to show stall speed) at
14:23:50 stalls at about 7 m/s
14:24:40 same, about 7 m/s
14:25:03 same, about 7 m/s

has throttle-off manual mode landings, 7.5 m/s (to show rudder authority at idle throttle and this low speed), at
14:25:57.5 - 14:26:02
14:27:59 - 14:28:05