The following guidfe applies only to IL2 cliffs of dover. il2 1946 does not have this kind of FF support.
either one of 2:
1-THe logitech profiler is failing to initiate at game start. Try putting every sldier to 0 and going in game: is the stick flat and effortless? good, jump to 2, is it still stiff as a rock? then try setting up your profile to global and head to the G940 forum in logitech- i cnat do more for you sorry
2-If your stick profile is actually working than its just a case of fine tuning your stick. I dont know you and your knowledge on the matter, so please dont take me wrong if i over explain things: Self centering is just an overral strength aplied to the stick independent of the plane motion. In real life if you are on the ground the stick will nto center it self and will fall with gravity ( upward), but as soon as you pick up speed it will get as stiff as a rock and hard to move. SO, try sitting yourslef in a plane on takeoff, if your stick is light here, and as soon as you take off go stiff, its working nicely as intended, if its stiff on the ground, back to 1. Some other behaviours yoour G940 will have who are a result of FF : in a stall the stick will go light as a father and in a spin will be pulling to either upper left or right, and not center, if you loose a wing the stick will go either left or right etc.... Once again if you test any of these and the stick is always in the same stiffnes, back to 1.
this is all i can do for you i think. If oyu still want issues try to find me in Steam as E69_Pupo, and i will arrange a TS server to help you further