I know it sounds a bit crazy, but! Our BMax does this from time to time. And I have deduced, correctly, that it is to do with the fuel! It depends on the "slosh" of the fuel in the tank. I haven't gone into the baffles in the tank of newer fords, not just the bmax, but our Kuga has a tendancy to do it too.
Check the fuel level, bumps and speed your doing.
1.6 tdci, remapped to 120 bhp, Panther Black Titanium with rear view camera, nav pac and front sensors. Always willing to stop & help in any situation I can. Karma is a beautiful thing.