Unexpected Loiter on Land Waypoint

Hi all.

I tested auto land feature on my UAV. It did well on the first and second flight. The log may seem weird in its takeoff part, but it is because I customized of runway takeoff feature to achive water-takeoff with differential thrust.

But on the next flight, vehicle did not go to land waypoint as desired and started loitering, though the mission was same as the previous ones. After one and half circle, it seems to have tried to land into wrong place.

The vehicle crashed afterwards due to gust and tip stall. But the main problem here is the unexpected loiter at minimum loiter altitude.

On first thought it was GPS failure or something, but no message was logged and I am at a loss now.

Do you have any suggestions? Thanks in advance!

The loiter altitude seem to be 25m, which is set by MIS_LTRMIN_ALT.
What kind of event may trigger loiter at this altitude?