Oh, so this is a global issue affecting everyone. If I understand correctly, the turbulence during missions is currently too extreme, even it's set to "Low", and it can't be completely turned off either. Based on the feedbacks I've read, this is something Asobo (Microsoft) need to fix, and there's absolutely nothing I can do about it.
Of course, I do have some understanding of turbulence, as I've traveled by plane and participated in several (or sightseeing) scenic flights, but I've never experienced anything like this, where the turbulence effecting the aircraft so much that it becomes nearly uncontrollable.