With a large control surface you want a servo and linkage system with enough "holding" power to prevent flutter.

The idea is to have the servo immobilize the control surface in the commanded position, even though airflow is working against this.

You are using relatively weak aileron servos, and I'll bet there is some play in the linkages.

The combination of the two permits the aileron to wiggle as the plane speeds up, in a harmonic fashion.

As things progress the servo can no longer hold the aileron in place and the aileron ( or any other surface ) can rip out.

Use a stronger servo or a digital one, with bigger linkages to help.