I found now the solution for my problem with bouncing after landing (sky-hero spyder 700 with Pixhack v3) and falling on one side.
As I was not happy with the Loiter performance I reduced the default Loiter PIDs as follows:
P: 2,0 -> 0,6
I: 1,0 -> 0,3
D: 0,5 -> 0,1
After that tuning my Loiter and GPS Hold was perfect. I did then Autoland and the Copter landed without bouncing and it switched off. I repeated then 5 times, no issues.
I then used the old Loiter parameter, the problem was back (3 times).
Why this correlates,I don‘t know. Developers could perhaps answer.