On this run I had really low FPS performances, I run at 60fps most of time but with an already used craft I ran this one between 10 and 20fps especially on map.
May the explanation be that I saved the last craft on a crash course, then re used same design with this flight
That is typically the cause. When your previous launches are loaded into the flight view at the same time, it can cause a performance hit. The severity depends on the complexity of the crafts.