Other than individual control issues, jerky fingers and the like, it may be elevator servo's breaking down. They do have wear and tear on the inside with feed back loops (potentiometers). You can also have connector points beginning to have corrosion and you lose signals or voltage to the servo, that would be more of an intermittent kind of issue. Sometimes dielectric grease can prevent some of that kind of thing on connectors. Bear in mind the elevator is used a great deal more as a flight control compared to the other servo with perhaps the exception of the wing servo's. And if you are using two wing servo's, sometimes one can break down and you can still fly with problems at least long enough to land.

I know I had a rudder problem for a while and figured out it was dumb thumbs. Once diagnosed, I learned to compensate and sort of retrain my brain and that problem went away. Flutter could be an issue but somehow I do not think it would carry from aircraft to aircraft. I still go back to servo internals breaking down. That seems to be the weakest link.