Its the band on wing.
your loading the wing at the bottom of the loop and in the corners.
The leading edge of the wing lifts, changeing the incidence momentarily.

put your wing on, lift the L.E. while pushing down on the front dowel. if it lifts easely use more bands.

a better solution is to convert the wing/fuse to a bolt on set up.
simply addind bands will work, but you may break the dowels at the bottom of a loop[X(]