On the SB13, the pitch oscillation was discovered to couple to the bending mode of the wing. The spar was therefore build with hogh modulus fibres (a first in aviation) in order to push the bending frequency out.

The pitch oscillation could be mostly suppressed by moving the cg aft.

Which then resulted in a very nasty stall behaviour due to span-wise flow on the swept wing. Boundary fences did help on that.

All in all, tricky optimisations. Plus a complicated lay-up plan for the swept-back spar in order to get the torsional load into the wing skin.