I have finally gotten everything to work nicely in an HIL, Flying the RC model in X-planes, APMplanner 1.0.9, Loaded latest APM through planner, solved all kinds of quirky problems proudly on my own, managed to start missions and the model flies nicely through all the waypoints but when closing in on the last ones, it suddenly turns to home and flies erratically and crashes into home base. This repeats with uncanny certainty, be it few waypoints or many. Always leaving the mission before the last few.
Cannot find out whats happening...
Here's a view I managed to save shortly before the mission failure after passing waypoint 21 in a 24 WP mission. It was supposed to fly on and return to home but suddenly took a 90° turn left towards home.