Dutch roll--oscillatory stability :when an aeroplane is yawned it rolls (with a swept wing there is a marked rolling tendency with yaw).
The fin and rudder then oppose the yaw,slow it down and stop it,and return the aircraft towards straight flight.
Design of the fin and rudder will determine if this roll is stable or unstable,resulting in divergent motion.
To correct a dutch roll motion you should apply one firm ,not big,correction to the aileron controlling the upcoming wing.(in and out,don't keep it).Then again,if necessary. It is not advised to use rudder to correct dutch roll,the roll is much visible than the yaw,so easier to correct.
And I guess you were correct,maybe an aditional efect on the swept upcoming wing by the yaw motion,not only that it travels faster,but also modifies the angle to the airflow,resulting lift..
brgds...