Boat start to runaway after the end of mission

Hello , I don’t understand a new problem with my ardupilot:

The parameter MIS_DONE_BEHAVE is set to Hold or manual.

So after reaching the last waypoint the boat stop, but several seconds later it start to go forward straight…

What can be the problem?
Here is a link for the log : I don’t have any idea of what data I need to analyze for that problem.

Thank you in advance

It’s set to manual (3). Set it Hold (default 0)

I already tried both with same result

Please help ?
I tried to reset the params to default but …
When I switch to auto with juste a “delay” waypoint, the throttle goes to 50 % but the param is set to 30 % . and the mis done behave param is not working…

I don’t understand : even if I set all the speed and throttle parameters to 0, it still send a pwm value of 1500 to the motor when I switch to auto…