Problem solved, it was subdle but I finally realized what happened.
The core problem is that generator was switched down at some moment of the fly and, after around 30/40 minutes, the engine shot down. In missions when I was able to reach the target electical system was not enoght powerfull to allow bombs to be dropped. I checked armament configuration, mixture, magneto, temperatures but I didnt looked at the right panel.
It was subdle because during startup I always enable the generator. In my wingwing f18 handle trim cross can be pushed, and I never assign a function to this push because can be activated accidentally. Anyway, I dont know why but generator switch was associated to the push of the cross I use for the trim.
I flown the mission and I was able to drop bombs (I had to bail out against f190 but this is another story).
Thanks for support and sorry if I bother you with this issue.