As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT HAD AN AIR TURNBACK DUE TO UNCOMMANDED RAPID LEFT RIGHT YAW MOVEMENT FOR APPROX 3 SEC NO EICAS OR WARNING LIGHTS OR INDICATIONS ON STATUS PAGE NOTICED AFTER THE EVENT. NO TURBULENCE ENCOUNTERED WITHIN THE GENERAL TIME OF THIS EVENT.