I just made some flight testing to see what is wrong. Results of this flight testing goes like this:

-I slightly advanced the CG
-I added some up thrust
-I sealed the elevators

I made all those changes at the same time, as was not recommended above, I don't know what really helped. I may suspect sealing the gaps helped somewhat since gaps were rather large due to 3D movements and big robart hinges.

I have now readjusted all my knife edge mixes since they were off due to those changes.

I still have some down pitching when I roll inverted. It seems to be worse when, just after the snap (still talking about the goldfish) I roll inverted full throttle but with low speed. This leads me to think I should add more up thrust. Is that possible ???

Thanks