Hello Belgian (from another Belgian fellow in Florida!)
I had similar problem with my YS63 (old one) in a Flip3D. It was getting warm inside the cowling and the problem resides in the regulator getting stuck and dying while hovering, with the negative results it produces.
I envisioned creating an airflow over the regulator but ended-up removing the cowling completely, since then no problem.

That's why the newer YS63 (and others) moved the regulator to the front where it has plenty of air.

Hope it helps

Ben