I can not tell from your video but you may have some negative Ackerman built in. If so, this can be very hard on the servo and cause such problems. You want absolutely no Ackerman or some positive. Positive is safer and will not cause any problems. Akerman, if you do not recognise the term, is the geometry of the set up. You want the line not being pulled to go a bit slack as you move the servo off center yet be just barely snug when at neutral. You do this by having the attach point on either the servo arm or the surface horn being offset from a line through the hinge point. If you Google Ackerman, you should be able to find a detailed explanation of it.