I am running into an interesting problem using a headless scene graph and bullet physics for server side.
My issue is that my player does not seem to change position. It will not even fall. It is using a BetterCharacterControl.
generally bullet will work fine on headless, but for debugging, why not simply changing to a non headless and enabling physics debug mode? Might help to see what actually happens.
Did you attach the physical objects to the bulletappstate?