RE: My plane experiences snaking
I had a large scale aerobatic model with an aerodynamic mass balance tab on the rudder. It snaked a lot till I cut it off and fixed it to the fin. This made the rudder smaller and the fin larger. Complete cure. Didn't change the look of the model either.
The linkage should be solid of course as should the servo mounting. If the rudder can flex then that could be it.
Also make sure there is no large air gap at the hinge point. Seal it up if you can.
You could try taping some tabs on the rudder just to see if that helps, then you can remove or change them easily.